I have noticed similar issues recently.
I noticed two types of behavior, either downloading does nothing and doesn’t provide any indication something went wrong, or I get a generic error about not being able to download the subtitle.
With verbose logging turned on, this is what I see in the Plex server console when I go to download a subtitle.
Nov 17, 2024 18:54:49.599 [139744012766008] Debug — Request: [10.23.10.10:58248 (WAN)] GET /library/metadata/486525/subtitles?language=en&title=King%20of%20the%20Hill%20(1997)%20-%20S05E18%20-%20The%20Trouble%20with%20Gribbles%20%5BDVD%5D%5BAC3%202.0%5D%5Bx265%5D.mkv (28 live) #79945 TLS GZIP Signed-in Token (gravee) (GRAVEE) / Accept => application/json / Accept-Encoding => gzip, deflate, br / Accept-Language => en / Connection => keep-alive / Host => 10-23-87-202.0f509af5ac6a46b1b387c0ef20567a47.plex.direct:32400 / Sec-Fetch-Dest => empty / Sec-Fetch-Mode => cors / Sec-Fetch-Site => cross-site / User-Agent => Plex HTPC; 1.67.1.233-0ab7ab17; Windows 10 Version 2009 / X-Plex-Client-Identifier => zjr1asdsadasda5 / X-Plex-Device => / X-Plex-Device-Name => GRAVEE / X-Plex-Device-Screen-Resolution => 1920x1080 / X-Plex-Device-Vendor => Plex / X-Plex-Drm => widevine:video / X-Plex-Features => external-media,indirect-media / X-Plex-Language => en / X-Plex-Model => Gecko / X-Plex-Platform => windows / X-Plex-Platform-Version => 10.0.22621 / X-Plex-Playback-Id => caeb372c-6b49-4919-a682-78ab15e835f5 / X-Plex-Playback-Session-Id => 2269e6e0-8■■■-45cc-ab9f-f13a5e9a85a0 / X-Plex-Product => Plex HTPC for Windows / X-Plex-Session-Id => 55ebec0c-7c10-4e7d-99d3-95f4cc3fb83a / X-Plex-Token => xxxxxxxxxxxxxxxxxxxx / X-Plex-Version => 1.67.1.233-0ab7ab17
Nov 17, 2024 18:54:49.677 [139744307690296] Debug — Completed: [10.23.10.10:58248] 200 GET /library/metadata/486525/subtitles?language=en&title=King%20of%20the%20Hill%20(1997)%20-%20S05E18%20-%20The%20Trouble%20with%20Gribbles%20%5BDVD%5D%5BAC3%202.0%5D%5Bx265%5D.mkv (27 live) #79945 TLS GZIP 77ms 791 bytes (pipelined: 15)
Nov 17, 2024 18:54:51.217 [139744003173176] Debug — Request: [10.23.10.10:58248 (WAN)] PUT /library/metadata/486525/subtitles?key=%2Flibrary%2Fstreams%2F2790142&codec=srt&language=eng&providerTitle=OpenSubtitles (26 live) #79d10 TLS GZIP Signed-in Token (gravee) (GRAVEE) / Accept => application/json / Accept-Encoding => gzip, deflate, br / Accept-Language => en / Connection => keep-alive / Content-Length => 0 / Host => 10-23-87-202.0f509af5ac6a46b1b387c0ef20567a47.plex.direct:32400 / Sec-Fetch-Dest => empty / Sec-Fetch-Mode => cors / Sec-Fetch-Site => cross-site / User-Agent => Plex HTPC; 1.67.1.233-0ab7ab17; Windows 10 Version 2009 / X-Plex-Client-Identifier => c46u5675675673rzr / X-Plex-Device => / X-Plex-Device-Name => GRAVEE / X-Plex-Device-Screen-Resolution => 1920x1080 / X-Plex-Device-Vendor => Plex / X-Plex-Drm => widevine:video / X-Plex-Features => external-media,indirect-media / X-Plex-Language => en / X-Plex-Model => Gecko / X-Plex-Platform => windows / X-Plex-Platform-Version => 10.0.22621 / X-Plex-Playback-Id => caeb372c-6b49-4919-a682-78ab15e835f5 / X-Plex-Playback-Session-Id => 2269e6e0-8■■■-45cc-ab9f-f13a5e9a85a0 / X-Plex-Product => Plex HTPC for Windows / X-Plex-Session-Id => 55ebec0c-7c10-4e7d-99d3-95f4cc3fb83a / X-Plex-Token => xxxxxxxxxxxxxxxxxxxx / X-Plex-Version => 1.67.1.233-0ab7ab17
Nov 17, 2024 18:54:51.229 [139744003173176] Debug — [Req#79d10] Activity: registered new activity d96c7fb3-ac4d-4711-b424-5171b5316df3 - "Downloading Subtitle"
Nov 17, 2024 18:54:51.229 [139744141708088] Debug — [Req#79d10] Downloading subtitle from https://metadata.provider.plex.tv/library/streams/7957832?X-Plex-Api-Token=xxxxxxxxxxxxxxxxxxxx
Nov 17, 2024 18:54:51.230 [139744309799736] Debug — Completed: [10.23.10.10:58248] 200 PUT /library/metadata/486525/subtitles?key=%2Flibrary%2Fstreams%2F2790142&codec=srt&language=eng&providerTitle=OpenSubtitles (26 live) #79d10 TLS GZIP 12ms 298 bytes (pipelined: 16)
Nov 17, 2024 18:54:51.581 [139744141708088] Debug — [Req#79d10] Got a subtitle of 99 bytes.
Nov 17, 2024 18:54:51.643 [139744012766008] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:51.643 [139744012766008] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:51.643 [139744012766008] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:51.864 [139744084446008] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:51.864 [139744084446008] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:51.864 [139744084446008] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:52.086 [139744003173176] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:52.086 [139744003173176] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:52.086 [139744003173176] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:52.311 [139744029530936] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:52.311 [139744029530936] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:52.311 [139744029530936] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:52.530 [139744020982584] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:52.531 [139744020982584] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:52.531 [139744020982584] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:52.749 [139744000252728] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:52.749 [139744000252728] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:52.749 [139744000252728] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:52.974 [139744007392056] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:52.974 [139744007392056] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:52.974 [139744007392056] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:53.194 [139744070662968] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:53.194 [139744070662968] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:53.194 [139744070662968] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:53.422 [139744020982584] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:53.422 [139744020982584] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:53.422 [139744020982584] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
Nov 17, 2024 18:54:53.643 [139744109452088] Debug — We're going to try to auto-select a subtitle for account 1.
Nov 17, 2024 18:54:53.643 [139744109452088] Debug — Subtitles: Found a candidate subtitle language [en] for a foreign film
Nov 17, 2024 18:54:53.643 [139744109452088] Debug — Audio Stream: 2520509, Subtitle Stream: 2520574
I remember there used to be a setting to set an opensubtitles.org api key for downloading subs, did that get removed at some point?