Keep losing internet

A couple weeks ago I bought a new cable modem, Arris surfboard, SB6190, and Google nest WiFi. Since then, our internet works great but keeps going out without warning. Today we have lost internet connection no less than 4 times. Rebooting the modem will bring it back, but it always goes out again a few hours later. I'm about fed up with Comcast as I rely on internet for work. Please help?!?