I have seen this is not a new issue for Xfinity/Comcast. We have been having this issue for so long, we just assumed it was normal. But it isn't and it is so irritating. We have been through every troubesooting imaginable. Changed the box. Changed the cables. Used "advanced support" on the phone.
I have finally gotten a tech to come out next week.
What were the prior solutions (if any) to this issue?
Pixelization is almost always related to a low signal or noise in the line. It can be caused by a spitter in your system, a bad cable, loose connection, or interference from another electronic device in your home. An in house tech visit should be able to locate the issue and fix it. I know for me, it was necessary to add a power amplified splitter at the house connection, to boost the signal to the lines inside the house.