Did some more testing.
Doing a Plex dance fixed most cast photos, but actors that appear in several shows have their photos reused even if they have different photos on TVDB. Don’t know if Plex is supposed to use photos from each show.
Elaborating on the music issue, I have two music folders. One for artists with full albums, and one for artists I only have some singles from. The full album library has the issues with certain artists not selecting the local artist poster and album covers. Interestingly it’s the same artists not selecting the local artist poster every time.
The second folder seemingly has no problems at all, loading the local artist poster and the album art from the music files. Tried to add a cover.jpg to one folder, and it was immediately loaded on a metadata refresh.
Trading places of the two doesn’t change the result.
Now the actually interesting part. If I move an album folder out of the artist folder, rescan the library and then put some of the songs back directly into the artist folder, not in an album folder, and rescan again … the proper artwork is selected from the embedded cover art in the music file.
Edit:
The bad artist poster looks like some caching issue for me. Of the four artists I have that do not load the local artist-poster, three of them use the displayed artist-picture in Windows’ folder preview. As they don’t contain the picture displayed right now, and it wouldn’t go away, I remade the folder and moved over the music and they now work.
I still don’t know what’s going on with the fourth artist. I did the same thing there, but to no success. It won’t recognize that there’s a local poster in its folder. I even tried to add other artists’ posters and other file names, like cover.jpg and poster.jpg.
Edit 2:
Looks like it’s a caching issue with the folder art as well. Recreated the folders and moving over the files, and now it works.
Still don’t know what causes that one artist to not find local artist posters.
Edit 3:
Copied the poster for the artist I was having problems with and named it artist-poster.png, and suddenly Plex finds it. Remove the .png and refresh library and metadata, the proper image stays. Remove artist from library, scan files, clean bundles and trash, re-add artist, proper artist poster loads.