Server Version#: 1.21.1.3766
this bug, annoyance has been around for quite a while. When you manually refresh metadata on an album, a second copy of the local artwork is added. (logs attached at bottom of post)
I believe Plex stores copies of the artwork someplace in the multitude of folders it creates for items in your library, and if that’s true, I really don’t need multiple copies of the same image stored in several locations on my hard drive.
Initial poster selection:
Poster selection after “Refresh Metadata”:
This is an image I created myself, has never been uploaded to any web site, so I’m quite sure it can’t be an image downloaded from an external source. The library is configured to use local artwork and metadata.
Related bug: If you try to match the album, and it fails, the artwork disappears, so you have to refresh metadata to get a poster to show. And you get the duplicate artwork…
attached logs: (File removed)

