I don’t know if the solution that was done on my mother in laws home would work in your case but, Time Warner came in and added a signal booster that was connected to a switch box. She has four rooms with digital tv through coaxial coming off the pole.
the man they sent over said first the signal degraded because the splitter/switch box was shot. He put a new box in the ceiling from where the cable comes in. He then took another small powered box that plugged into the power 110 outlet and ran a coaxial cable into the new switch/splitter and also went to each connection into her set top boxes and replaced the ends. After this was done he reset each tv box, one at a time tested the screen for pixilation and none was present.
all the others were done and it seems they are all fine now. So it maybe you need the ends that connect from the splitter and to the boxes replaced.
This is just an idea. If it worked for cable it may work for Fios tv.