Xfinity has pushed either new firmware or new settings to the XB7's that is causing issues with smart home devices.
The new firmware has taken down things that used to work in our home:
If you reset the modem to factory defaults, you'll see that things start to behave properly again until such time that Xfinity pushes their change again (happened to us within 24 hours).
When was the firmware that broke everything? Bc i know we got one 2 nights ago. But I couldn’t connect my lifx bulbs b4 that firmware So it is the xb7 I have to go back to the xb6. Xb7 has had nothing but issues for me. Ill try it again in a year
The two WiFi bands have recently been combined into one with the Comcast gateway devices. Some devices get confused and don't know how to see / talk to combined bands.
If you are not using any Xfi Pods, you can try separating the 2.4 and the 5.0 bands and give them two different broadcast names / SSID's;
Associate the devices with the 2.4 or the 5.0 (whichever one it needs) band's SSID (broadcast name) and password.
I have the CGM4331COM model of the XB7 (found under the My Account app and then Internet)
We found out that unplugging the modem and allowing it to remain unplugged for 15 seconds and then plugging it back in seems to have cleared whatever was causing the issue. We had attempted to unplug and re-plugin before but not waited the 15 seconds (Xfinity actually calls for 12 seconds in their guide). Afterwards my LiFX bulbs, printer, wemo plugs, etc.. all miraculously came back to life.
Not sure if it was directly firmware related or just some other change that had occured to the modem.
You have to let people at xfinity know that ax is causing issues and users should be able to change wifi modes in settings.
Customer service needs to know
I'm not a CC employee. Just a lowly volunteer here. You can lead a horse to water, but.....