Are you having issues with a streaming stick or Ultra? I had issues with a streaming stick, switched to using the supplied power adapter from the TV's USB port (as suggested above) and haven't had any more issues so far, knock on wood.
I have the same issue with my Ultra and after chatting with someone from customer service, and they just went through the basic routine of unplugging power, resetting unit, factory resetting unit and so on, I decided to remove the Micro SD card from my unit before factory resetting and all of a sudden it started working fine. Rebooting stopped and now it's fine. Not sure if there is a file in my Micro SD card that is corrupt or there is an issue with the unit accepting the card but so far so good. I will get a new Micro SD card and see what happens. I probably don't need it because the unit has enough internal memory for now.
This may be the issue. I will give it a week without reinstalling SD card and see what happens. Hope that helps.