Plex does not index albums where the first track has a different Artist from the main AlbumArtist

Investigate other albums. Sometimes “missing” tracks are merged into existing albums.

Investigate the content of the AlbumTitle meta tag. It must not contain the disc number. There is a separate meta tag for this.

I forgot: if you find that several albums of different AlbumArtists have been intermingled, you need to Plex Dance all albums of all involved Album Artists.

That’s OK. The Artist in the file name of my examples was partly a stand-in for the corresponding meta tag – just to illustrate it better.

Check the meta tags also for missing or empty “Track Number” tags.