Collections don't have thumbnails

[Twiglet]

Try this: Go to Dashboard-> My Plugins ->TMDb, and ensure all Image Scaling options are set to original. These settings affect the TMDb Boxset plugin, even though they are separate.

Thanks this was the issue for me. The image scaling defaults in the TMDB plugin are all blank so the image search doesn't work until you go into the plugin and set them.

I was confused by this problem because all my movies and TV series had succesfully been assigned images, but I've now realised that that's because they were falling back to other image fetching methods like TVDB, OMDB etc.

It seems that the issue stems from the fact that the only image fetcher available for the Collection library is TMDB, but the defaults for the TMDB plugin make the plugin non-functional for image fetching.

I also had to unlock metadata for my collections like another poster mentioned. I definitely didn't lock it as I only just installed Jellyfin today for the first time and didn't touch that setting so it must have defaulted to that.