I noticed that Live Channels app updated while I was out of town, and using it now forces the audio out to HDMI for me. Is this happening to anyone else? All other apps will go to Bluetooth audio devices when connected but Live Channels seems to ignore that route.
I used to have this in Plex when I had AC3 Passthrough enabled in my Android TV audio settings. If the source was stereo, it would go through my Bluetooth headphones, but if I chose to watch a movie on Plex that was encoded with 5.1, the sound would come blaring through my receiver at FULL volume, waking my family. TV stations broadcast 1080p/5.1 surround, so I bet this is what's happening. (To test this, try some other channels, like one of PBS's 480p/2.0 sub-channels.)
Somewhere in the HDMI settings there's a pass-through setting. Play with that and see if that changes anything. You might also look for some audio settings in the Live Channels app itself.