I am having this problem as well. Mine will go down sometime between 12:00 AM and 12:20AM and not have any ability to recover. I have to restart the modem for it to reacquire an internet connection.
It doesn't happen every day -- sometimes every 3 - 4 days, sometimes two days in a row. When it does go down, regardless of when I last restarted the modem or our internet usage, it goes down ALWAYS during that timeframe.
After back-and-forth with both Comcast and Arris and a tech visit to verify any signal issues, I'm of the opinion that it's a trash modem from Arris. The difficulty is going to be getting them to take it back or I have to eat $200+ loss.