I know this sounds weird, but maybe you can help me anyway:
I run the most recent Plex version (1.5.3.3580-4b377d295) available for my Synology NAS with DSM 6.1.1-15101 Update 2. This week, I purchased a Plex pass and I think since then, I'm not able to stream TV series to my TV anymore. When I hit play, the TV app enters full-screen and display the navigation controls in the bottom half of the screen but the screen itself remains blank. So I thought, I give the "optimize" feature a try. TV shows I've added before purchasing the pass are being optimized correctly. All recent episodes added after the purchase can't be optimized and I get the error "Invalid Metadata" (as attached): 
In the main menu, I already tried Libraries > Clean Bundles, Empty Trash and Optimize Database. I already restarted my NAS and Plex server application.
What I think is strange is the fact that "old" episodes are displayed and streamed correctly. So I created a new TV shows library and pointed the library-directory directly to one show's folder. Now trying to stream from that new library with old episodes, none can be played. But the same episodes can be streamed in from the other library where they have been imported before I purchased the pass.
The file-endings are either .mp4 or .mkv, both don't work anymore. The files are organized flat as /[Show Name]/Show.S12E20...mp4 or /[Show Name]/Show.S12E21...mkv (however, as said, previously that wasn't an issue as covers, seasons and episodes are displayed correctly).
Could you please help me resolve this issue? I assume you eagerly await some log-files. Which ones should I upload and where do I get them from? Could it be an issue with Agents?
For the new library, I picked "TheTVDB" and in Settings > Server > Agents > Shows > TheTVDB I ticked "TheTVDB", "Plex Theme Music" and "The Movie Database".