Pixelation happens when the signal for the channel you are trying to watch is too weak or has too much noise. This is most likely due to a poor connection between the box and Comcast's network, usually in or near your home. It may seem odd that only one channel is affected, but techs see this every day.
Troubleshoot by checking all connectors for corrosion and tightness, and by looking for damaged coax cable. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power.
Be aware that if the Comcast tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have their Service Protection Plan (https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast cable box/DVR/digital adapter or anything outside your home, you shouldn't be charged.
Hi there, @JGard911,
We wanted to reach out and touch base with you to make sure the pixelation is no longer happening. If so, can you please private message me your full name? Thank you for posting to our forums.
To send a private message, please click my name "ComcastMartin" then select "Send a Message" on the right side.