Latency spikes, disconnections, unstable connection

I'm on a 300Mbps plan with the XB7 modem, which I was given recently when I upgraded my speed. Since adding the new modem, I've experienced random interruptions while connected through ethernet and Wifi when streaming video (buffering animations), random Wifi disconnections,  and disruptions while playing games, both on my PC and through Geforce Now. 

I've contacted Xfinity support several times, and each time they have me reboot the modem and verify connections and the quality of the cables, they send an updated config file (I don't remember if that is the correct term), and they have provisioned it at least three times now. 

I ran some packet loss tests, and one of the tests showed an 18% packet loss. The connection status, while playing through Geforce Now, for example, shows packet loss in the hundreds and I can see the latency numbers through Geforce spike for several seconds before returning to normal in between these spikes. 

The issue occurs with both ethernet and Wifi. I have ruled out the issue involving too many devices using my connection by allowing only my PC to be connected to the XB7. The problem still persists. Any help would be appreciated as, thus far, Xfinity insists on running the same troubleshooting steps that have not fixed the issue for almost a month now, and troubleshooting steps or solutions never go any further.