XB8 5 GHz WiFi much slower than 6 GHz despite full gigabit speed to gateway

Hi, I’m having a performance issue specifically with the 5 GHz Wi-Fi on my Xfinity XB8 gateway.

I have the 1 Gig plan, and the Xfinity gateway speed test shows approximately 1,002 Mbps reaching the gateway, so the internet connection coming into the gateway appears to be working correctly.

I split the Wi-Fi bands so I could test them separately. Using the same iPhone:

• 6 GHz: ~563 Mbps

• 5 GHz directly beside the XB8: ~214 Mbps

• 5 GHz in the next room: ~187 Mbps

• Xbox Series S on 5 GHz: ~150–155 Mbps, despite 94–96% signal strength and 0% packet loss

The Xbox cannot use 6 GHz, so the poor 5 GHz performance is significantly limiting its download speeds.

I checked the Xfinity app, but the XB8 is automatically managing the 5 GHz channel, channel width, and other radio settings, so those settings are not available for me to adjust.

Could an Xfinity employee please check the 5 GHz radio/configuration on my XB8, including channel selection, channel width, congestion/interference, and whether the gateway needs to be reprovisioned, optimized, or replaced?

I’ve already restarted and tested the equipment and devices. I’m specifically trying to troubleshoot why 5 GHz is substantially slower than 6 GHz even when the device is directly beside the gateway, while the gateway itself is receiving the full ~1 Gbps service.

Additionally, my Xbox reports Moderate NAT and “UPnP not successful.” Please also check whether UPnP is functioning correctly on the XB8 and whether anything in the gateway configuration is preventing the Xbox from obtaining Open NAT.

Thanks.