Get rid of splitters and/or use amplified splitters. If you have your own added splitters, make sure they handle the high frequencies needed for cable nowadays. The old cheap splitters "just work" for analog channels (you might get some snow), but can easily make digital stations unwatchable (no signal or this kind of problem).. and yeah, it happens on some channels.
Our house has enough splits that I needed to put in my own amplified splitter to even GET most of the digital channels. I think I still miss some I'm supposed to get, but at least it's usable on most that I care about.