Music albums not grouping correctly in iTunes on iPhone
Several people have reported the problem that in recent versions of iTunes on iPhone some songs are not grouped correctly as albums, even when the tags are complete and correct.
For me, the following was the simplest workaround that I found, and as as far as I can tell it has not been mentioned yet (apologies in advance if I overlooked it):
I noticed that in the case of albums that don't sort correctly, in the "sorting" tab the "artist" field entry is grey, ie it was entered automatically, which is normally enough, and iTunes for OS X interprets it correctly.
If you add it again manually (as you would normally only do if you want it sorted differently for some reason), then the songs will be grouped correctly on iPhone as well.
Annoying to have to do that for lots of albums, but it works and perhaps it also helps to identify the cause of the problem.
iPhone SE, iOS 12