Of course everyone isn't affected, but IME with Comcast, it took 3 different box swaps to get the Moto 6412 working correctly. FWIW, I just downgraded one box to a SD DVR and so far (luckily) it doesn't need to be replaced.

My vote is, try another box and hope for the best. Ideally you would not have to wait for an installer and simply exchange at a local Comcast office. This is a easier way to get what you need IME. Hooking up the downgrades is easier too.