There is a known issue with TheTVDB agent and Plex is working with the service to get it back to normal. Plex said in a post that it might take a few days.
Some episodes are still being matched and some are not using TheTVDB agent.
I found that the episodes which failed to match for me got matched by manually selecting The Movie Database agent for the unmatched episode, or series.
This problem should be effecting everyone, and there are multiple posts with users reporting the same issue.
Hopefully you weren’t one of the users that thought uninstalling Plex and starting over new would fix it…
I’m not sure I would recommend changing the agent for a TV series already matched with the TVDB agent. Past experience has ended up with duplicate entries whenever I change the order of agents. I’m inclined to wait it out till the fix is in, even if this workaround does the trick.
It’s a very annoying issue, as I watch all my shows from On Deck, and unmantched episodes don’t show up in On Deck. Sure hope this fix propagates soon, as I just tried to match them individually again, and no luck so far.
