I also experienced the on/off problem with this box from Comcast months ago. I had multiple Comcast service tech come to my house and try to fix it and finally they did.
Basically, the tech on site worked on the unit with guys in remote offices for over 2 hours. They were trying different software patches and box settings and everything seemed in working order. Unfortunately, about 2 hours after the tech left, the box "rebooted" itself.
I left the box alone for 1-2 more days with periodic restarts, and then noticed that during one of the restarts, the channel display on the front had a message (I remember it as something like "P1") and a blinking cursor. That lasted for about 3-4 minutes, as I assume it was some type of patch push by Comcast, and when the box came back on, the problem was resolved. It has been months and the box has been stable.
All I can say is that somewhere within the labyrinth of comcast, someone knows how to fix this problem. I am in the Detroit area is that helps.