For arbitrary reasons, Apple Music will: remove songs from albums and re-add them to your library as the "single" or "deluxe" versions; split albums and intersperse tracks between both; and duplicate songs in albums.
The albums usually still exist in Apple Music—I just have to go out of my way to remove the mangled music and re-add the album. Problem is, there is no warning or notification it happened.
Examples:
[1] https://pasteboard.co/K2kdUN3.png This album is totally messed up. Multiple track 3 with different titles, one unavailable, missing tracks that were re-added to my library as singles.
[2] https://pasteboard.co/K2keFBV.png One song pulled out into a greatest hits compilation and duplicated
[3] https://pasteboard.co/K2kfc0b.png All tracks, except 1, removed. The album still exists in Apple Music.
[4] https://pasteboard.co/K2kfBTR.png Originally added the original version of Camp by Childish Gambino to my library—here it's split between deluxe and basic, with tracks arbitrarily mixed between both.
[...and many more]