Music is all lumped into one album named "Various Artists"

Plex Media Server Metadata & Adding Files
7

I don’t think you need to do much more debugging as I spotted the likely issue.

  1. Don’t change the metadata within the plex UI which is for special needs and a band-aide when we need to cure you.
  2. You have to fix your Music file naming structure to conform to the current Plex standard. It’s very sensitive to that. The track xml you linked showed the naming is an issue, and when that happens your music lands in Various.

Please follow this for an entire Artist as a test:

  1. Move a whole artists material out of where plex can see it on the drive.
  2. Plex dance (scan library files, empty trash, clean bundles, optimize db)
  3. Rename the files correctly.
  4. Put the files back onto the USB music location
  5. Scan Library files.
  6. On that artist Refresh Metadata and beer.

Example

Music/ArtistName/AlbumName/03 - Some Song.mp3