Pixelated images when viewing recordings on my DVR

When viewing a recording on myX1 DVR box, the picture is often pixelated. If I rewind & replay I  find it is the same place that the pixelation is occurring. If I watch the same recording on my phone using my Xfinity App  there are no issues. I have recently done the system refresh. I checked to make sure all my cable connections were tight. My guess is I have a bad hard drive my X1  box when I go to Comcast, labs and check my Cable strength that always says good. I’m pretty technologically savvy and I would like help from someone who is an official Comcast representative before I go and replace my box