Google Nest Community

This is the way. Leave HDMI-CEC off if your TV doesn't support it, and the problem goes away.

I think I may have found where the glitch is. I disabled HDMI-CEC as my TV doesn't support it anyway, and so far the issue hasn't come back. Fingers crossed.

A month later and I still have to reboot my Chromecast every time I leave the room for a few minutes.