I removed the .jpg files from the folders, but that didn't matter. It's still wrong and missing.
Perhaps I should have posted in the bug forum instead.
Anyway, so this is an issue since 2019? Seems like it could have been fixed by now if it comes up so often.
Here's MusicBee displaying two different album arts for the SAME song at the SAME time (again, it switched back to 100% wrong a few seconds later):