I seem to be having a continuous problem with how music is being picked up within my Plex library. I have all of my music tagged properly within Apple Music (iTunes) thus:
Can you verify if Apple Music has written that metadata to your files? Sometimes the data is in their database and displayed correctly in their app but not accessible to others.
Also… did you change the metadata after you added the files to Plex?
I’m not aware of any issue in this area.
Given you’re using this legacy agent which is supposed to only use local metadata… could it be some of the first files you added for that artist don’t have complete artist metadata or have listed this artist in its short form?
If they’re all in the same top-level artist folder, Plex will probably attempt o apply that to all albums contained in the folder.
You could create a separate library using the Plex Music agent (should be the default for a new library). Configure it to prefer embedded metadata (as in your screenshot) and point it to the same music folder. This way you can verify if this is handled better with the newer agents.