I'm having a similar situation that other users have reported. The xfi app isn't working following my installation of a new gateway received from Comcast.
Does the new gateway appear in My Account?
Yes, including two previously used devices that are no longer needed.
What are the two devices? I had some old devices on my account and I called 1800comcast and they were able to remove them. Maybe they are what is causing your issue.
I am having the same issue. Help!
I just took a look and it appears the issue may have resolved itself. Can you please try accessing xFi and let me know if you still experience an error?