TV pixelation when running Internet Speed Test

Hi. I am having and issue where the tx pixelates / freezes. This seems to only happen on a few channels 841, 842, 843. I contacted Comcast last week and was told the channels themselves were having issues and the network team would fix it. It has been good now for a week, but is back now. Whats weirder is that if I run the internet speed test from the xfi app on my phone, during the upload portion of the test, the pixelation is terrible. I can make the issue happen with the speed test. I have the 600 mps speed package.