Does this happen on all your TVs? Can you move the stb to another location to see if the trouble follows?
The pixelation can occur for a number of reasons. It could be wiring, splitters, ont, or even a low signal on your fiber.
You can make sure all the connections from the ont to the set-top box are tight. Make sure there is no red video light in the ont. If still occurs after troubleshooting you will have to contact verizon.