When using the Personal Media Artists agent (or any agent, other than “Plex Music”), Plex depends heavily on the folder/filename structure of your files to identify them and match them to MusicBrainz. This is true even if your embedded tags are very accurate and your library is set to “Prefer local metadata,” as yours is. Plex’s requirements for file organization are here:
Adding Music Media From Folders | Plex Support
If your tags are very accurate, the “Plex Music” agent is much less dependent on the folder/filename structure than the other agents.
On a side note, I see you have “Store track progress” enabled in your library. This setting is helpful for audiobooks, or really long music tracks (like a complete album in a single file), but not so much for typical music libraries.
