Severe local WiFi packet loss/latency to Xfinity gateway – Ethernet is clean

Please mind the ChatGPT summary, as we are past my level of understanding of the issue, and I am doing the best I can... 

I’m looking for help diagnosing what appears to be a local WiFi issue with my Xfinity gateway/network that standard Xfinity diagnostics have not detected. This happens occasionally but, specific to the last few days, Zoom and Microsoft Teams have experienced significant intermittent lag. Normal streaming and speed tests generally work well. I’ve spent considerable time troubleshooting with Xfinity support, and they report that the signal into the house, modem connection, device connections, and service all look healthy.

The gateway was replaced a few months ago, and the Xfinity WiFi extender is also relatively new (approximately 1–2 months).

I’ve now been able to reproduce and isolate the problem by continuously pinging the local Xfinity gateway at 10.0.0.1 from the same MacBook.

Test 1 – WiFi, Xfinity extender ON

• 2,472 packets transmitted

• 3.1% packet loss

• 5 ms min / 42 ms avg / 1,970 ms max latency

• 170 ms standard deviation

Test 2 – WiFi, Xfinity extender OFF

• 2,550 packets transmitted

• 5.4% packet loss

• 3 ms min / 238 ms avg / 4,367 ms max latency

• 799 ms standard deviation

Test 3 – Same MacBook connected via Ethernet

• 2,541 packets transmitted

• 0.0% packet loss

• 1.4 ms min / 4.1 ms avg / 165 ms max latency

• 6.3 ms standard deviation

The MacBook reports a strong 5 GHz WiFi connection, generally around -47 to -59 dBm RSSI, with high PHY/Tx rates. Apple Wireless Diagnostics also showed a generally strong connection. The Ethernet comparison seems particularly significant to me: the exact same computer communicating with the exact same gateway has 0% packet loss and ~4 ms average latency over Ethernet, versus 3–5% packet loss and severe latency/jitter over WiFi.

Interestingly, removing the extender made the results substantially worse, so the extender does not appear to be the underlying cause and may actually be improving the connection.

My question: What could cause this level of packet loss and latency between a device and the local Xfinity gateway despite excellent reported WiFi signal strength? Could this indicate RF/channel interference, an issue with the gateway’s WiFi radios/firmware, channel width or automatic channel selection, or another Xfinity WiFi configuration issue?

I’d appreciate help from someone who can look beyond WAN signal levels and speed tests and help diagnose the local WiFi/RF side of the gateway, since the controlled WiFi-vs-Ethernet testing seems to isolate the issue there.