Been having this problem for a while but, after updating to iOS11 on the iPad and the latest plex apps on the iPad and AppleTV, I thought I would bring it to the forum's attention. I have a movie synced to my iPad. I can play it locally there without problem. I want to stream it to the plex player on the appletv so I choose it as a player in the iPad's plex app (it is shows both "This iPad" and "Plex for AppleTV"). But I am immediately told "Uh-oh! Something went wrong playing your media. Please try again". This happens everytime.
I can turn on AirPlay mirroring on the iPad to the AppleTV and stream that way but would much prefer to plex player streaming instead of mirroring my tablet.