I'm experiencing intermittent packet loss and latency spikes on my Internet connection

I'm experiencing intermittent packet loss and latency spikes on my Internet connection. It happens roughly every 10-20 minutes and causes high network jitter while gaming.

I've tested with my PC connected directly by Ethernet to the Xfinity gateway, so my third-party router is completely bypassed. During the problem, the gateway 10.0.0.1 remains stable at around 1 ms, but I get packet loss when pinging external addresses such as google.com or cloudflare.net. I've confirmed this isn't specific to one destination. My connection speed is normally around 700 Mbps down / 170 Mbps up. A Waveform bufferbloat test gives me an A, although the download test occasionally shows latency spikes as high as ~322 ms under load. I also checked the gateway's DOCSIS signal levels. Downstream power is as low as -15.7 dBmV on one channel and around -8 to -10 dBmV on several others. Upstream power reaches 49.5 dBmV. I've checked if there was any damage on the coax cable running to the box outside of my house but there doesn't seem to be any. This started around the time there was maintenance in my area. Could you please check my modem's signal levels, upstream/downstream error counters, and the node/CMTS for intermittent packet loss, upstream noise, or ranging issues?