All you have to do is LISTEN to what the overseas call center tech is telling you.. get up and check those connectors on the back of all your receivers, did thatwork ? no it did not , ok unplug the receivers for a minute and then plug it back in again, this will reset the system.. Great did that work? ok you may have to do this 10 -15 times a day to keep the service up and working ,, PS <Edited> to be helpful do not ever call comcast because there is no way to keep a record of what they will tell you,, ALAWAYS use the CHAT and save a copy of each and every one , <Edited>,, YOU PAY THEM FOR A SERVICE <Edited>
I have the Xfinity TV box and it is happening across all of my TVs on specific channels only.
the problem you describe can be before or inside your home wiring. A field tech will have the meter necessary to test outside your home to determine the problem.