I’m having this exact same issue on Synology DSM 6.2 (xpenology). I have tried clearing out the plug-in support caches, and even completely removing the plugin along with the plex folders. I’ve adjusted the permissions, and the plex user has full control over my TV shows directory. I’m hoping that somebody can help out with this.
Edit:
This forum post may have shed some light on this issue. Looks like there were some changes to the TVDB API.
Thanks, hopefully once that is corrected it will resolve my issue also. I fear my problem was something else since it’s been that way for several months but if this fixes it I’m good.