I recently got a firmware update for XFi that broke my wifi and I have a temporary workaround. This firmware upgrade was supposed to increase my internet speed from 400/10 to 500/15.
Temporary fix: Use the XFi mobile app to use different SSIDs for your 2.4 GHz and your 5GHz networks.
Xfinity rolled out a firmware upgrade to me 2 days ago to increase performance, and also to encourage the use of their mesh network (see XFi Pods). In this upgrade, they started enforcing that the 2.4GHz and 5GHz networks use the same SSID. Using the 10.0.0.1 interface, you can no longer separate the SSIDs, but you still can make this change from the XFi app.
The new firmware upgrade however, causes problems when the SSIDs are the same - I am getting dropped connections all over the place (I often don't have an IPv4 address, and when I ping a remote host, it is unsuccessful about 80-90% of the time) making the internet anything but usable. Once I split the SSIDs, it works great on each SSID/band individually, with solid connectivity and high speeds. Prior to the firmware upgrade there was no problem when they were on the same SSID.
To make the change in the app, I click on the network name (SSID) on the main page, click Edit Wifi, check the "Use different names and passwords for 2.4 GHz and 5 GHz WiFi", and then put in a different name for your 5GHz network. It is no longer possible to do this on 10.0.0.1 directly, and according to the tech who came to my house this morning, this functionality is by design and intended to promote the mesh networks. He said my network is being monitored for 30 days and then they will probably propose to send me Pods. It wasn't broke before, and I support the use of the mesh network, but right now, this solution isn't working. If the firmware isn't fixed and I can't separate my network SSIDs, I don't have a working network anymore.