I’m not absolutely certain, but it is my understanding those come from the movie, or show as it resides in your library and is the default when no other poster is available or able to be downloaded in a correct match.
What happens if you edit the item right there? Is there no other poster image available there either? It is getting a background image - unless that too is derived from a local screenshot.
Grasping here - try ‘Optimizing’ the database - from the same place you Clean Bundles.
And the ‘Arthur Murray Dance School’ instructions for ‘The Plex Dance’ are as follows:
Remove Media
Update Library
Clean Bundles
Empty Trash
Correct Media Name and/or Structure Before
Return Media to Library
Update Library - or allow an automatic update and rediscovery.
… and just as another grasp - Reboot the server box - just because you can. Couldn’t hurt.
I just read a post from @sa2000 regarding a somewhat similar issue wherein he suggests:
You can try clearing cache
https://support.plex.tv/hc/en-us/articles/202967376-Clearing-Plugin-Channel-Agent-HTTP-Caches
That too couldn’t hurt.
