Modem/router randomly disconnecting after setting up xr500

Hello,

I recently installed the Nighthawk XR500, using my Xfinity modem/router as a bridge (which I changed in the Xfinity gateway settings).

Everything works as expected, however, I am experiencing random disconnects from my modem. This issue has never occurred before so I know it is due to the new setup. Essentially, the "online" light on the Xfinity modem will turn off randomly (each of the three times has been during an online game using my Xbox), cutting off my connection to the internet. The light will either stay off or start blinking, but never get back to solid unless I unplug the modem and power cycle it back on (which takes around 15 minutes). Once the "online" light comes back on, full function of my network is restored.

Is there any way I can assure that this stops happening? It seems to be due to using the Xbox (connected to the Nighthawk via ethernet) because it did not happen when I wasn't using it. Perhaps it is something with the way I set up QOS?

Thanks for any help.