I had this issue (on Catalina / Apple Music after Sync Library) because of the "Compilations" flag was set on some tracks and not others or some other inconsistencies in the album data causing it to get split on the phone, but Compilations was a huge culprit. Physically in my library on my Mac either part or all of an album would end up under artist "Compilations" instead of the true artist. Cases where part of the album was erroneously under Compilations corresponded to cases of split albums on the phone. This would happen even when it wasn't various artists e.g. best of xyz would end up under Compilations directory instead of xyz directory, despite being under artist xyz when viewing it in Music app. In some cases I didn't even need to change data just open up Get Info and Apple would figure out it was in the wrong place (at some point - maybe with the Catalina upgrade - Apple must have changed how this stuff is stored to be under Compilations instead of Various Artists. and my library became inconsistent).
See if this is the case with your examples and if there is consistency in album data on the songs in particular that Compilations flag. The fix is to open Get Info on the album or all tracks at once, and toggle the flag to off (or on, but not a mixture).
And also check what is stored under Music/Compilations to see if they are really compilations.
