CM Error Codewords

The number of uncorrectable bit errors increases with the total uptime of the modem. It's cumulative. Looking at yours, that is a very small amount when compared to the total number of unerrored bits passed. Are you actually experiencing any connection problems or are you just curious ?

 As a test, does a computer / device that is hardwired directly to the router / gateway device with an ethernet cable have the same "dropping" problem ?

With this test, we are trying to isolate this down to being either a WiFi-only problem or a problem with the general connection to the Comcast system which would of course affect both. It's a good first step in troubleshooting before proceeding any further. 

Some tips for improving WiFi performance;

http://corporate.comcast.com/comcast-voices/10-ways-you-might-be-killing-your-home-wi-fi-signal 

https://forums.xfinity.com/conversations/internet/answered-how-to-improve-your-xfinity-wifi/602da486c5375f08cd804f16 

https://www.xfinity.com/support/articles/improve-your-wireless-home-network 

https://www.xfinity.com/support/articles/internet-connectivity-troubleshooting?linkId=180985598 

There are other options. Google for WiFi repeaters / range extenders, WiFi mesh systems / pods, powerline ethernet adapters, MoCA adapters. Good luck !

https://www.cnet.com/how-to/home-networking-explained-part-2-optimizing-your-wi-fi-network/ 

https://www.smallnetbuilder.com/wireless/wireless-features/wi-fi-ping-spikes-causes-and-fixes/ 

1,698 Uncorrectable Codewords is very low, if that is over a day or more. Based on your other replies it seems the main issue is really WiFi problems.

I can't seem to find a way to manually set the Wifi channels in either the XB8 Gateway Web UI or via the Xfinity mobile app. Did some searching and it looks like they lock this down unfortunately. The best you might be able to do here is find out if your XB8 is picking a bad channel or not. You can use the Wi-Fi Spectrum Analyzer in the XB8 http://10.0.0.1/wifi_spectrum_analyzer.jst and/or a Wifi Analyzer app on Android or iOS to see what kind of channels it is picking and what the overlap is. Then you could report that to Xfinity support if it is picking overloaded channels often.

Not sure which device(s) you are using on Wifi, but have you tried updating the operating system and WiFi drivers on it?

Ethernet will always be more stable than Wifi, especially in an apartment. I would recommending moving your cable gateway to a cable jack that can allows you to wire in while gaming. If that isn't feasible I recommend looking into MoCA, the XB8 has a MoCA feature you can enable, then pick up a MoCA adapter so you can use ethernet with it in another room.