I wonder whether it is right place to insert my comments btu decided to give it a try for the very frustrating issue.
Same thing here for about three years after having brand new line from the box on the street to my house and alll new cables in the house too.
I think it is. handshake issue within the Comcast netwrok server and the last point of contact.
I am not professional on that but, I can see there is nothing wrong with the cables and also it is measured by the technician 2 days ago.
I also got new wi fi 3 modem from Xfinity and same thing got worse. I got connection for few mintues and it is gone in the next minute until I re-start or reactivate the dateway.
I really need help on that. Otherwise I am looking for a new service provider in the negihborhood.