That's truly odd. The comcast modem I have has battery backup power and has never restarted in 2+ years. Something is truly amiss here.
I don't see it but thought I'd add a thought here.
Ever since we got a new Panasonic Dect 6.0 wireless phone system, phone calls have suddenly dropped. We have a Belkin N+ router and an Arris modem through Comcast. The modem just kicks out, the router kicks out, then the Modem and router automatically restart and the phone works again.