Inconsistent episode thumbnail creation

[cornucrapia]

I'm getting some confusing behaviour with episode thumbnail generation in jellyfin. This is happening with all my episodes so I'm picking a show and season at random to showcase here.
Episodes up to a certain number (this varies by season/show but around 5 or 6) will have the correct thumbnail, but then episodes after that will all have the same one of some episode in that series.
Each episode has a thumbnail file associated with it that's mapped to it in the nfo. For example:

Make Some Noise (2022) - S01E01 - HBOs A Game of Rock Paper Scissors [WEBDL-1080p][AAC 2.0][x264]-BTN.mkv
Make Some Noise (2022) - S01E01 - HBOs A Game of Rock Paper Scissors [WEBDL-1080p][AAC 2.0][x264]-BTN-thumb.jpg
In the nfo: <thumb>https://artworks.thetvdb.com/banners/v4/episode/9214443/screencap/62a84ce45dd5e.jpg</thumb>
which goes to the correct thumbnail that matches the content of the downloaded jpg.
This is the case for episodes that display the correct thumbnail and for episodes that display a different one.
If I refresh and replace all metadata including existing images it will not change things if I don't take any other action.
If I manually select a particular episode and "edit images", search for a replacement image and download that one (which will be correct) redoing the refresh and replace all metadata including images
will change which episode thumbnail the incorrect shows are receiving (including the one I just manually selected) but otherwise won't change the result, a few early episodes in the season will have
correct thumbnails, the others will all share one episode's thumbnail from that season.

I'm running jellyfin 10.10.1 in a docker container using the linuxserver image. The thumbnail presentation issue is present in web, mobile (iOS) and AndroidTV clients

I've got the tvdb metadata plugin installed. For metadata readers I have NFOReader at the top, YouTubeMetadata is also listed but shouldn't be used since they have NFO files
I don't have any metadata downloaders set and for image fetchers I recently turned on the tvdb downloader to test replacing images
I have "save artwork in media folders" checked so it should be expecting to read images from the location I mentioned above
The metadata is originally generated by sonarr if that's relevant

Watching the logs when I do a refresh I see some messages about processing subtitle files but nothing about images

This was working before, although I honestly didn't notice exactly when it stopped, it might correspond with a jellyfin upgrade but I can't be totally sure

Any suggestions for further troubleshooting or solutions would be appreciated

[TheDreadPirate]

Can you "replace all metadata" on one of these shows and once that completes share the jellyfin log via pastebin. Can you also share screenshots of the library settings. Specifically the metadata providers and what order they are in.

[cornucrapia]

I can, but in the meantime I turned off sonarr metadata, turned on the tvdb as a provider and enabled nfo saver in my library and rescanned everything. This is now working for the most part, although the two seasons I've checked have had one episode that's missing an image. I can manually download that image and then a replace all metadata will persist it. That's weird. Does any of that change suggested troubleshooting steps to follow up on?

[TheDreadPirate]

Are you using alternate episode ordering? The default is the order they aired in. If you're using something other than the that and that results in more "seasons" than the aired order that may explain why some entire seasons don't have the correct thumbnails.

[cornucrapia]

I'm just going off whatever the tvdb grabs, sonarr and jellyfin should be using the same ordering and organizing them the same. And it's not the last episode in the season that it does it on. One season I'm looking at it's the 9th out of 10 episodes and another it's the 17th out of 22. Exactly one episode per season in all the shows I've checked.

[cornucrapia]

Ok doing some more testing on recently added series. They all start with the same episode image for that season, although which episode it is appears to be random. If I trigger a refresh and reload all images all episodes will get their correct image, except whichever episode they were all using for a cover will be blank. I can then go to that episode and edit images, search for an image and get an updated image. If I replace all metadata including images a second time everything will stay fine.