TV Pixelation

This is a repeat issue.  Tech visit recently tried but was not able to fix the problem.  He removed amplifier that was installed on the line by Xfinity years ago, removed a filter on the line, checked the connection to the street, disconnected unused lines in the house.  He said signal strength is good.  Box is new.  HDMI and cable connections are new and wires were supplied by Comcast.  Internet and phone are working properly.  Phone support keeps wanting to reboot my box which does not solve the problem.  This problem started about one month ago.  No problem when streaming.  Pixelation happens on life connection and on programs recorded to DVR.  Pixelation happens at repeatable times on recorded programs.  I would like to get this elevated but can't get past phone support.