During the daytime, I like to keep my TiVo box turned on all the time so the hard disk doesn't keep spinning down and up while in standby (this, in my opinion, causes it to fail sooner). I turn the box to standby overnight so it makes less noise.
Frequently I find that the box has either switched itself to standby after being left on, or has turned itself on to full power overnight while I've been asleep. I put the remote control in a drawer so I don't accidentally press any buttons. I've also had a couple of overnight recordings 'split' as if the box is doing a reboot or something while recording.
Is anybody else having issues like this? Are there any kind of Power Management options you can set for the box? This particular box has a hard drive with a VERY loud click when it spins up or down, and can actually wake me up if it happens overnight!
Sorry to learn about the inconvenience you're experiencing lately.
You can find some information about the power saving options [here]. I'd recommend turning your power saving options off to ensure the set top box doesn't put itself into standby, you can do that by following:
Help & Settings > Settings > Devices > Power Saving Settings
As to the box turning itself on, it could be part of the updates that happen late at night occasionally but it's not something we'd expect to continually happen, does this happen often?