Unstable internet connection on one device after upgrades

I upgraded to the fastest plan Xfinity offers, which required upgrading to the XB7. On the day after I upgraded, the laptop closet to the new router started having connection stability issues. The connection is unsuitable for gaming or streaming just on that one device now. I've made sure Windows and the WiFi adapter drivers are up to date. There were no problems with the connection stability until the upgrades. 

Can someone help me figure this out?