“Clean Library” didn’t work to clean up the duplicates. What ended up working was going to video configuration and deleting all other sources I’m not using. All my movies in an external HD attached via USB to my Odroid C2. I don’t need the other default sources.
The problem with the missing covers persists, though.
I’ve deleted the thumbnails cache as you advised and it didn’t work.
Tried changing scrapers again, followed by “clean library” and reboot and it didn’t work either.
That’s pretty weird.