Searching for Signal?

Two of my three tvs are having problems receiving adequate signal. It is sporadic but most frequently occurs during high usage times or high view programming.  Sometimes there is no picture, sometimes there is pixellation, sometimes the image from another channel bleeds over. I have TiVOs on both of these tvs (different models) and yet another TiVO on the tv that is fine. Comcast has come out twice. The first time I was told it is because of congestion on the lines since so many people are home during COVID. The second time I was told that I need to replace the cabling in the house. I question why two separate cables would fail at the same time while the third cable is just fine. The technician told me that the amp boosting all three cables is fine. Before I spend the time looking for options other than Comcast, or before I spend the money to run new cable, I would like some suggestions as to how I can diagnose whether this is related to neighborhood congestion, bad cables, bad amp, or TiVO compatibility. Thanks!