Sounds like low signal and/or bad connectors at the Dmarc (box on the side of your house). On main TV Hit the XFINITY button, then select the settings icon (at the far right side) then choose COMCAST LABS then SIGNAL STRENGTH and see what you get when you are getting the error. I had a similar issue and they replaced the drop from the main box next door into the Dmarc box outside and all has been fine. YMMV
They can also remotely test your signal levels hpwever if it is a bad cable or termination it may be fine when they test.