Intermittent issues, especially where there's no obvious common factor, makes me question what the rest of the system looks like, and if there's a potential common factor that's not obvious. In this case, given the high case temperature involved, I'd be looking for something power-related (either on the source side of things, or on the load side of things). I could see scenarios where a bad HDMI or USB cable, or combination of cables and equipment, could cause the observed behavior.
Not sure you'll be able to find a definitive source of the problem without being able to reproduce the issue on command, though. So my next steps would probably be to take a broader look at the system if it happens again - try setting up the exact same system (including cables, power supplies, monitors, etc.) back at the shop to see if it is reproducible in a controlled environment.
