I had problems like this with several multi-disc albums. Ultimately, I laid the blame on Gracenote and last.FM, because they never seem to have consistency in their tagging. The only thing that got my discs in order was to make absolutely sure my embedded ID3 tags were correct and complete, and I configured Plex to use them.
Just to be sure, there are a couple of things to do to get Plex to use embedded tags. You’ve probably already edited your Library and enabled the ‘Use embedded tags’ option. But you also have to arrange your metadata agents in the correct order. Make sure the ‘Local media assets’ agent is at the top of the list for Artists and Albums:
In your ID3 tags, it’s important that the Artist, Album Artist (even if it’s blank), and Album title are identical in each file, and that the disc number is correct in each file.
This screenshot is from EasyTag, the ID3 editor I use:
Once you’ve done all that, and especially if you had to edit ID3 tags to get there, you’ll probably need to do the ‘Plex Dance’ afterward to get Plex to read them in correctly. (The Plex Dance is a workaround for a problem that has existed in Plex seemingly forever. It should be embarrassing to Plex that they have such a major problem that has hung around for so long that the workaround for it actually acquired a name, but here we are)
Let us know how it goes.
