Using the xfinity.com/activate link worked for me also.
I recently returned and replaced a Comcast issued Modem/Wifi gateway > activated the new modem over the phone > had the issue everyone is seeing in this thread. Xfinity TV app is recognizing the new modem.
Solution - After activating the modem over the phone > I used the earlier suggestion to activate the modem online > after doing that, everything is working again.
I spent over 1:45 minutes with several comcast techs, with no solution. They are unaware to search forums and find it easier sometimes to pass customers off to another department. They need a good knowledge base to reference.
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