Hi my name is Nico,
I am running Plex Media Server v188.8.131.5222 and I am still having this issue with videos in the Watch Later section not being able to play through the web app. I can watch them on mobile and chromecast them but I am unable to watch them through the web app. This has been an ongoing issue since the previous version of Plex media server.
Hope you guys can fix this.