Edit: My apologies, messed up the list of topics 
This should have been posted in the Windows forum as a reply to this topic: https://forums.plex.tv/discussion/247645/metadata-not-downloading-in-full-if-at-all#latest. Can someone move it?
This problem (or at the very least, a closely related one) is still present in 1.4.2.
I upgraded yesterday from 1.2.7 (to which I reverted a couple times as it was the “latest” version that never exhibited this issue for me) and again Plex appeared to be unable to load information from TheTVDB.
tl;dr: It appears that somehow the certificate for *.plex.tv is not accepted as a valid certificate by Python on my Windows Server 2012 machine. Manually “trusting” the certificate solved all my issues.
More details: When trying to refresh a show (Sleepy Hollow in this case) using 1.4.2 from Plex Web, the following is reported in com.plexapp.agents.thetvdb.log:
2017-02-25 13:08:27,584 (f8c) : DEBUG (networking:166) - Requesting 'https://tvdb2.plex.tv/login'
2017-02-25 13:08:27,615 (f8c) : INFO (logkit:16) - JWT Error: (<urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)>) -
2017-02-25 13:08:27,631 (f8c) : DEBUG (networking:166) - Requesting 'https://tvdb2.plex.tv/series/269578/images?lang=en'
2017-02-25 13:08:27,645 (f8c) : INFO (logkit:16) - Problem with the request:
2017-02-25 13:08:27,645 (f8c) : INFO (logkit:16) - Bad image type data for TVDB id: 269578
Throwing the “JWT” error-message in Google yields a lot of generic Python/SSL related issues, amongst them this post on Stack Overflow: http://stackoverflow.com/questions/30704894/why-i-receive-certificate-verify-failed-from-google-adwords-api
This go me thinking it might actually be related to a broken trust-chain on the Windows Server 2012 machine I have running Plex. So, I downloaded the SSL certificate from https://tvdb2.plex.tv (which is the certificate for *.plex.tv, so it doesn’t matter which domain you get it from) and added it to the certificate store on my server.
Et voila, TheTVDB agent again works flawlessly.
For those interested in the workaround: You can easily download the SSL-certificate from https://tvdb2.plex.tv using Firefox (with Chrome not so easy). Instructions on how to add a certificate to your Windows’ certificate store are here.
