Sorry it took me a while to get back to this. I updated to MC26.0.88 today to get this change:
26.0.88 (6/3/2020)
10. Fixed: Setting current audio program as default when playing live TV on a client did not work.
That works now. I played Live TV on the Client, changed from PID 103 to 104, the MC Client locked up with the Buffering message, I selected "Use current audio stream as default", then stopped Live TV playback, restarted it, and PID 104 was correctly selected. The channel and new Audio Program played as well, but I had the "Buffering" message on the screen. So I stopped playback on the Client, closed MC on the Client, waited a while. When I reopened MC on the Client and then connected to the MC Server the Live TV started to play immediately! PID 104 was still selected, but I didn't select Play on the channel. It was obviously still playing on the Server and just continued when the Client reconnected. But at least the "Buffering" message was gone.
Unfortunately, I didn't log that event.
Anyway, back to the issue at hand; The freezing on the Client when the Audio Program is changed. I changed the Television log verbosity to 2 as requested.
This time, I already had PID 104 selected as the default Audio Program, so I selected PID 103. The video didn't lock up with the "Buffering" message this time, but no audio played. So I saved PID 103 as the default Audio Program again, to replicate the tests I had done before exactly.
I will attach the Server and Client logs from this test here and post the second test separately.