I tell Google Home something like "Hey Google - Play Sia Videos". It starts playing to the default Chromecast device, plays 1 or 2 videos, then stops and disconnects from the Chromecast device. Why?
Looks like I have this solved. The Chromecast was disconnecting and going back to home screen after some period of playing. It felt hot to the touch. I added ventilation to the cabinet and stuck a heat sink on it and it has not disconnected since. It seems to have been overheating in the enclosed cabinet. Maybe this will help someone else...