A picture speaks a thousand words:
Obviously this is the Beatles album "Revolver". All the tracks are mp3s and are tagged properly and consistently. They're in a folder named "Revolver", which is in a folder named "The Beatles". I copied these files into my Plex library from iTunes, which organized them correctly. Checked PMS's logs but didn't find any relevant info, other than that it scanned the Revolver folder. Near as I can tell, none of my other music albums are doing this. I do not have Plex Pass, so this is using the "last.fm" agent.
Any ideas what in the world is going wrong?