This is great debug information that you posted there. Unfortunately, the Plex developers haven’t come up with a solution for this. There is no response to this post either: How does Plex select album art to display
I guess the solution could be quite simple: allow setting a preferred album art filename (e.g. folder.jpg). Plex actually finds the local files (as seen in the poster selection dialog) but shows no clear pattern of choosing a file.
