Nighthawk X6S R8000P and CM1150V modem

Hello everyone,

I recently upgraded to gig speed with xfinity and purchased a CM1150V modem and a R8000P router . modem boots fine and everything seemed ok until i hooked the router. At first everything seems fine i get wifi setup and then connect other devices to the wifi.

my network is this 2 iphones 2 smart tvs on 5GHz band wifi a Xbox one x wired from router and a pc wired from router. out of the blue the upload will start blinking on the modem or the modem will start a soft reboot. when i say soft reboot i mean it starts from download then upload then Internet then phone. xfinity don't want to seem to help because signals are good. Any help would be great.

On another note , i can hook my old linksys ea6900 and have no problems.

Am i missing some setting in the router i need to change? i dont change no settings in the router but for the wifi names and passwords.