Thanks for the help so far.
I found my ways to the log files, and found that the issue seems to be that the Last.fm agent only retrieves a maximum of 9 potential hits, and that for some reason more than 9 other artists come before the correct one in the result set. Thus the agent never sees the correct artist.
By manually looking at subsequent artists, I could find the correct match in the JSON as hit #13.
Personally I would say the real issue here is that the webservice hosted by Plex that caches the Last.fm results returns fuzzy matches before exact matches. Although it is a deficiency that the Last.fm agent does not continue pulling results beyond the first 9, given that it discards all but one of the first 9 due to being poor matches.
Here’s the JSON file for the first batch of results, the only one the agent considers:
{
    "results": {
        "opensearch:Query": {
            "#text": "",
            "role": "request",
            "searchTerms": "abrahma",
            "startPage": "1"
        },
        "opensearch:totalResults": "138",
        "opensearch:startIndex": "0",
        "opensearch:itemsPerPage": "9",
        "artistmatches": {
            "artist": [
                {
                    "name": "Abraham Mateo",
                    "listeners": "36781",
                    "mbid": "ae44dccd-8fdc-42ff-84a6-2a0549bacca4",
                    "url": "https://www.last.fm/music/Abraham+Mateo",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/09ef0db3d1cd017cd266489db74b336d.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/09ef0db3d1cd017cd266489db74b336d.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/09ef0db3d1cd017cd266489db74b336d.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/09ef0db3d1cd017cd266489db74b336d.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/09ef0db3d1cd017cd266489db74b336d.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Troels Abrahamsen",
                    "listeners": "20296",
                    "mbid": "585bf499-0b7e-4463-b970-11c3d865f1c0",
                    "url": "https://www.last.fm/music/Troels+Abrahamsen",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/949bb0d6a3b743b992b5a98722c3b0d3.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/949bb0d6a3b743b992b5a98722c3b0d3.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/949bb0d6a3b743b992b5a98722c3b0d3.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/949bb0d6a3b743b992b5a98722c3b0d3.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/949bb0d6a3b743b992b5a98722c3b0d3.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abraham",
                    "listeners": "32618",
                    "mbid": "9ca0f936-67ee-48bf-b3e6-8fd4e9c469a4",
                    "url": "https://www.last.fm/music/Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/1d54f0b2f53c4366947052affb3dfd6e.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/1d54f0b2f53c4366947052affb3dfd6e.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/1d54f0b2f53c4366947052affb3dfd6e.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/1d54f0b2f53c4366947052affb3dfd6e.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/1d54f0b2f53c4366947052affb3dfd6e.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Jennie Abrahamson",
                    "listeners": "28163",
                    "mbid": "0e058e8d-702d-4879-9c5a-906daee7f75a",
                    "url": "https://www.last.fm/music/Jennie+Abrahamson",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/1f12b3157e4c41e2c1d0c5ae0002edb6.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/1f12b3157e4c41e2c1d0c5ae0002edb6.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/1f12b3157e4c41e2c1d0c5ae0002edb6.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/1f12b3157e4c41e2c1d0c5ae0002edb6.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/1f12b3157e4c41e2c1d0c5ae0002edb6.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Heights of Abraham",
                    "listeners": "33196",
                    "mbid": "c26cc89a-ce98-43b9-9537-3eed79403f6b",
                    "url": "https://www.last.fm/music/Heights+of+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/c867e0d799e14282ba1f7dba4a41ac08.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/c867e0d799e14282ba1f7dba4a41ac08.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/c867e0d799e14282ba1f7dba4a41ac08.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/c867e0d799e14282ba1f7dba4a41ac08.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/c867e0d799e14282ba1f7dba4a41ac08.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Ben Abraham",
                    "listeners": "21840",
                    "mbid": "",
                    "url": "https://www.last.fm/music/Ben+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/fde30cbc5e9dc7ecc2dd859eaaa5818f.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/fde30cbc5e9dc7ecc2dd859eaaa5818f.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/fde30cbc5e9dc7ecc2dd859eaaa5818f.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/fde30cbc5e9dc7ecc2dd859eaaa5818f.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/fde30cbc5e9dc7ecc2dd859eaaa5818f.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abraham Boba",
                    "listeners": "4101",
                    "mbid": "3f1c8461-a34a-4591-b60d-e3d8998dec87",
                    "url": "https://www.last.fm/music/Abraham+Boba",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/b5814a0f6474433b980537a9b6f575f1.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/b5814a0f6474433b980537a9b6f575f1.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/b5814a0f6474433b980537a9b6f575f1.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/b5814a0f6474433b980537a9b6f575f1.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/b5814a0f6474433b980537a9b6f575f1.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Leo Abrahams",
                    "listeners": "16820",
                    "mbid": "8dce9ad6-9415-4373-9747-dcac5ef43aef",
                    "url": "https://www.last.fm/music/Leo+Abrahams",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/fd6a3e8784c04d248863016393a4444e.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/fd6a3e8784c04d248863016393a4444e.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/fd6a3e8784c04d248863016393a4444e.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/fd6a3e8784c04d248863016393a4444e.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/fd6a3e8784c04d248863016393a4444e.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abraham Inc.",
                    "listeners": "5277",
                    "mbid": "b1d847ff-4f4a-4a18-88a8-73cf14aeca9e",
                    "url": "https://www.last.fm/music/Abraham+Inc.",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/7e0799a354b74e6586c67459a5c89201.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/7e0799a354b74e6586c67459a5c89201.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/7e0799a354b74e6586c67459a5c89201.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/7e0799a354b74e6586c67459a5c89201.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/7e0799a354b74e6586c67459a5c89201.png",
                            "size": "mega"
                        }
                    ]
                }
            ]
        },
        "@attr": {
            "for": "abrahma"
        }
    }
}
And here is the one for the next batch, where the correct artist is located:
{
    "results": {
        "opensearch:Query": {
            "#text": "",
            "role": "request",
            "searchTerms": "abrahma",
            "startPage": "2"
        },
        "opensearch:totalResults": "138",
        "opensearch:startIndex": "9",
        "opensearch:itemsPerPage": "9",
        "artistmatches": {
            "artist": [
                {
                    "name": "Vader Abraham",
                    "listeners": "17604",
                    "mbid": "a74bd336-7e59-4bdb-a33d-61073bdcfe44",
                    "url": "https://www.last.fm/music/Vader+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/aa0f6d125cc34ad0a41c0cf55a752943.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/aa0f6d125cc34ad0a41c0cf55a752943.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/aa0f6d125cc34ad0a41c0cf55a752943.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/aa0f6d125cc34ad0a41c0cf55a752943.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/aa0f6d125cc34ad0a41c0cf55a752943.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Farrah Abraham",
                    "listeners": "4213",
                    "mbid": "fcb4c7da-538b-41da-81a5-84072cd6568f",
                    "url": "https://www.last.fm/music/Farrah+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/ec2dfaa87e504761a21de772edae3652.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/ec2dfaa87e504761a21de772edae3652.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/ec2dfaa87e504761a21de772edae3652.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/ec2dfaa87e504761a21de772edae3652.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/ec2dfaa87e504761a21de772edae3652.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Josh Abrahams",
                    "listeners": "13621",
                    "mbid": "6bd8f0df-696e-4731-900a-12c1c842e724",
                    "url": "https://www.last.fm/music/Josh+Abrahams",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/f66dfca0dccf4bad893be19a724c6b28.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/f66dfca0dccf4bad893be19a724c6b28.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/f66dfca0dccf4bad893be19a724c6b28.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/f66dfca0dccf4bad893be19a724c6b28.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/f66dfca0dccf4bad893be19a724c6b28.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Andy Abraham",
                    "listeners": "12066",
                    "mbid": "4efb6fb6-eb60-4eb5-b01c-2a15cfa38562",
                    "url": "https://www.last.fm/music/Andy+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/8b6aa297b54c42347e7d29b22966abcd.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/8b6aa297b54c42347e7d29b22966abcd.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/8b6aa297b54c42347e7d29b22966abcd.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/8b6aa297b54c42347e7d29b22966abcd.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/8b6aa297b54c42347e7d29b22966abcd.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abrahma",
                    "listeners": "2398",
                    "mbid": "5ef6b315-73b4-4617-89ad-f3649afcba58",
                    "url": "https://www.last.fm/music/Abrahma",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/4c524090d693fd00f646edc060369a84.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/4c524090d693fd00f646edc060369a84.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/4c524090d693fd00f646edc060369a84.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/4c524090d693fd00f646edc060369a84.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/4c524090d693fd00f646edc060369a84.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abraham-Hicks",
                    "listeners": "1097",
                    "mbid": "d04bd4e0-5a96-47d5-90ed-e8c935a0ac85",
                    "url": "https://www.last.fm/music/Abraham-Hicks",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/308fced7b56b4b61b5bd492c1fe67a81.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/308fced7b56b4b61b5bd492c1fe67a81.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/308fced7b56b4b61b5bd492c1fe67a81.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/308fced7b56b4b61b5bd492c1fe67a81.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/308fced7b56b4b61b5bd492c1fe67a81.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Lee Abraham",
                    "listeners": "1670",
                    "mbid": "a217f5df-f9e3-4aee-b6de-599c5c2e6c7d",
                    "url": "https://www.last.fm/music/Lee+Abraham",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/8b85f63f9a6d460494a2ee570497ddcc.png",
                            "size": "small"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/64s/8b85f63f9a6d460494a2ee570497ddcc.png",
                            "size": "medium"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/174s/8b85f63f9a6d460494a2ee570497ddcc.png",
                            "size": "large"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/8b85f63f9a6d460494a2ee570497ddcc.png",
                            "size": "extralarge"
                        },
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/300x300/8b85f63f9a6d460494a2ee570497ddcc.png",
                            "size": "mega"
                        }
                    ]
                },
                {
                    "name": "Abraham Laboriel",
                    "listeners": "2975",
                    "mbid": "ea14ad72-eff5-4a21-934b-8b93f4d45d1b",
                    "url": "https://www.last.fm/music/Abraham+Laboriel",
                    "streamable": "0",
                    "image": [
                        {
                            "#text": "https://lastfm-img2.akamaized.net/i/u/34s/0f1ed9638f494c528c002d69c8bb5079.png",
                            "size": "small"
                        },
                        {
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