I've just thrown my test albums at it and the only thing it got wrong was to order 'Album 10' before 'Album 9'.
Box-sets (supporting DiscSubtitle), remasters (including one with the same Album, AlbumArtist and Date), multi-disc albums were all correctly grouped, so it must be heavily relying on folder structure.
I use FLAC, maybe I'll test with WAV, but yes it's almost certainly a tag issue.
One folder per album, with Album, Date and AlbumArtist always fully populated each having the same value across all tracks of an album is the way to go.