If it's been a while since its normal nightly self-reboot, it will do that. The way to keep it from self-rebooting is to keep it on Netflix, Prime or any other app. When it's in an app, even if you fall asleep and someone turns the TV off, the Hopper remains in the app, and the timer will not fire to reboot the Hopper.
The two conditions must not be active for it to reboot.
1) No recording is in progress or scheduled to be started at the reboot time.
2) If any App is in control.
So if the guide data and internal control data become too stale, it will refresh, and if it hasn't been allowed to reboot a couple of times, it will also go into full diagnostic mode, telling you to wait.
So, do you or your family happen to watch Netflix, Prime, YouTube or whatever during the nighttime? Or leave it in the app without exiting? If so, that's the problem. So either tell them to use the darn exit or live with the refresh.