Brand New 3TB Time Capsule shuts down approx 3-4 times daily

I bought a 3TB Time Capsule for my wife for Christmas 2014. I'm on Comcast BLAST Internet service in Northern CA. I use their Voice / Modem combo in bridge mode with the TC as the wifi router.

The TC just randomly shuts off daily. 3-4 times per day. Unplug, plug it back in, green light, works fine. Then a few hours later, green light off, have to unplug to reboot.

I already went to the Genius Bar once (mid-April) and they replaced with a new unit. New unit is doing it again. That led me to think that Comcast is somehow spiking or dropping signal and kicking off the TC. Comcast tech came out yesterday, no problems on their end. Smooth as glass, no problems. Plug the 5K iMac into the modem directly, no problems.

So I called Comcast and set up my old Motorola Surfboard modem (maybe this voice gateway is the culprit?) Had that Surfboard for three years with an old ASUS router; worked like a champ forever. TC is dropping on the Surfboard too.

Any wisdom out there from the Apple Tech Ninjas?