iTunes syncs songs as "Unknown Album" if songs don't have Album Artist set in iTunes

When iTunes syncs music to my iPhone, songs end up displaying i Music as "unknown album" if they do not have the "Album Artist" set in iTunes (one 'album' icon appears for each song). This just started happening with a recent upgrade of iTunes and/or iPhone Music.

The fix would be to just set the Album Artist on all these songs. But these are generally old songs that I imported from CD years ago and I probably have several thousand of them - so that's not going to happen.