How can I get correctly tagged tracks to show in a compilation album

I listen to dance music. Most of my collection is ripped to FLAC, and tagged properly. Despite this, PLEX regularly misses many tracks form a DJ mix.

For example, I have here a CD all ripped correctly. All tagged correctly. But only 1 solitary track appears in plex. This particular DJ mix is spread over 6 discs. I have both the WEB release, with over 80 tracks, and the CD I ripped myself, with around the same number of tracks. Yet on 1 track actually appears, and this single track is tagged no differently than any other track in the compilation.

Why, oh why, can I not just tell PLEX to look at a folder, and include all tracks from that folder in the album? Heck, the filenames and tags are already numbered too, so how hard could it actually be?

Here are some tips regarding music

multi-disc albums
https://forums.plex.tv/discussion/comment/1050849/#Comment_1050849

handling singles and EP’s
https://forums.plex.tv/discussion/comment/1093611/#Comment_1093611

possible ‘side car’ files for music
https://forums.plex.tv/discussion/comment/1319703/#Comment_1319703

soundtracks and ‘various artists’
https://forums.plex.tv/discussion/comment/1472799/#Comment_1472799