I just installed the new Xfinity gateway (router & modem), and lost my XfinityWifi hotspot, even though my web Xfinity hotspot page shows it's enabled. So, after chatting a while with Xfinity tech support, they said that XfinityWifi is disabled in my gateway and can only be turned on by Xfinity internal tech support (level 3, I guess, since I went through 2 levels on the chat), which will take up to 48 hours (and they'll call me when it is done). Hopefully all will be well soon.
Have you first tried powercycling / re-starting the device ? No joy ? Try hard resetting the device to factory defaults by pressing and holding in the recessed reset button on the rear for 30 seconds. You will lose any customized settings.