I am another dissatisfied customer with the same casting problem:
PLEX Media Server: 1.26.0.5715
Tuner card: Hauppauge WinTV-quadHD (Model 1651xx.1 Dual ATSC/QAM
I cannot find anything about this on the support site other than that I should be able to cast LiveTV from an IOS device or the web (not local) app. Neither works. I get the (universal) “Sorry” message with no other information than “Something went wrong,”
NOTE: I am able to cast recorded programming.
This is one of many problems I have with LiveTV and DVR functionality including but not limited to subtitles, backward scrolling, and general guide problems. Please solve the casting problem first (if I get a vote).