Since updating from 27.0.16 to 27.0.20 (and 27.0.21) I have this issue when playing live tv on a client. It's happened two nights in a row... After I'm done using the downstairs Tv (Server PC) for the night, I go to an upstairs tv (client PC), open the Guide and play a live tv channel, the screen displays the first frame of video and freezes but the sound continues to play. No buttons on remote work so I have to do CTRL-ALT-DEL on a keyboard, which reveals MC is "not responding". After killing and restarting MC, playing live tv works fine.
EDIT: I can verify the Tuner does release after killing/restarting the MC Client. And oddly, after this happens, a "time shifting" item for the frozen tv channel is left-over on the client only. In theater view it says "no actions available" for the show, so I have to go to standard view and delete the left-over time shift show.
Attached log file from the Client.