Hi, Steven and team.
I recently cleaned the artwork from all my tracks and let Musicbee research for them as I play the tracks. I observed that some albums that MB used to find the artwork for before are not being searched now. All the sources like Fanart, iTunes, etc. are active.
Example albums whose artwork is not being found:
Breaking Bad - Season 1
Batman: Arkham City
Kill Bill: Vol. 1
Version from Windows store: 3.3.7367