Disconnecting during online gaming

Good evening. I have a serious issue with disconnecting during online gaming. The game will run fine for a short period of around 10-30 minutes and then the game with disconnect from the server and the internet will freeze on all devices. The constant dropping from games is becoming increasingly annoying as I pay for high speed internet and should be able to handle the bandwidth usage. I currently have the 1.2mbs XFi package through Xfinity. I used to use bridge mode with my own router and had no issues until recently. The router that I was using was the Netgear Nighthawk XR500. Unfortunately it did not have all the specs to take advantage of the 1.2Gb speeds so I disabled bridge mode and ran off the Xfi modem from Xfinity. Since I have ran off the XFi router/modem combo the disconnects have started again. I have tried a DNS and IP flush, I've swapped ethernet cables, I have swapped COAX cables, done a few modem restarts and power cycles. No solutions as of this post. Streaming from the devices have no issues. I have also attempted port forwarding with no success. I will be swapping the XB7 modem/router combo out this week to see if the XB8 router/modem has the same issues. Are there any other solutions that can be brought my way before I buy my own modem and router and return the XFi completely. Please help!