Are you referring to the smartphone app or the website?
I am having same exact problem. xfi worked fine for months and then stopped last week. Cannot access from app or web and I know my modem is compatible (unless something has changed on Comcast's end). Have spoken to customer service, tried chat support, and no one has been able to figure it out. Very frustrating. If anyone has any answers it would be greatly appreciated.
Hi jc733, can you provide an update with the message you are receiving when you attempt to access xFi either from the web, app, or X1 xFi app?
If you are still unable to access, let us know and we can look into it.