Could it be that it is a various album and a single artist album where the artist is only in the various artists list like you typed in the 3 or 4 names of the different artists that were on the various album, ex: buck owens , roy clark, buck trent, johnny gimble.
And the single album was just johnny gimble.
If it was something like that maybe that confused the pathway?

My Music collection is set up with Album Artist, Album, Year, Rating, Location, and To Edit. The last two don't appear in the MMW sync list editor, which is just fine, and the other four do, which is just as I want it. I sync primarily with Album Artist, selecting individual albums underneath each artist name.

On MMA, in the Sync Contents option page, the folders and selection appear as they do on the MMW side.
Then, I add an Album under an Album Artist via those options, the MMW version of the sync list now shows Artist and Album Artist, with the new album selected under that tree. I expected it to be under Album Artist.