Symptom presented itself first on one of the Android 6.0 Leelboxes. It was working earlier today but then the spinning wheel when connecting to the stream simply fails to stop spinning. I later verified via browser that Live TV definitely wasn't working at all. At this point, I restarted Emby Server (just the software) and Live TV was working fine again. The attached logs are for all of today up to the point when Emby Server restarted.
This may be the second time this happened (there's a thread about it here but I can't find it). I believe the last time it happened was with 3.1.0.0 3.0.8500.
Edit: Found it: Latest beta can't manually log in
logs.zip