I've had this house for just a couple of years. All the cable wiring was in place already. Lots, and lots, and lots of wiring. The basement is 74 feet long. Cable comes in at one corner, runs the entire length, then returns along the opposite wall. Lots of extra cable in loops here and there. Splitters. I have one run to the cable box for the TV, and one to the internet gateway.
You said I should check connections. There are so many cables not being used, so many that go in strange directions, so many splitters... well, so far I haven't been able to make much sense of it.
The problem was happening yesterday evening, but I did mess with some connections. I will continue to keep an eye on the quality.