C3000 Wifi disconnects every 20 to 30 min.

I've had this modem/router combo since Feb. of last year and haven't had any issues.  Except today, my wifi has dropped almost every 20-30 min.  It's happened on all of my devices.  I have high speed internet with Xfinity.  I reached out to them, and they did a reset on the firmware. It still dropped, so it wasn't that. I unplugged my modem/router and then hooked it back up; it still dropped. Xfinity is going to send someone out here Thurs. to see if it's something to do with the pedestal or my modem/router. Has anyone else ever had this issue? If so, then is there something I haven't done that I can do on my end? Just to be clear, all of the devices lose connection not just my computer. (My iPhone, Roku, etc. all lose the connection).