I've been getting some weird freezes and odd behavior on my iPhone X as well. And I started with a clean install. Went to the Apple Store yesterday to have it checked out and the genius was pretty frank with me. He said that iOS 11 has has more weird little bugs like that than any release he remembers, especially on iPhone X, and he (jokingly) pined for the days of 10.3.3, which he believes was a highpoint of combined functionality & stability for iOS.The other day, running 11.1.2 or whatever it was prior to 11.2, my X did the same thing, but it also didn't respond to buttons, or tapping the screen. I had to do a hard reset to make it respond again. First time that had ever happened. Here's to hoping it doesn't becoming a recurring problem.
He said that I could reinstall the OS if i wanted, but he wasn't sure it would help. He said these weird iPhone X freezes and hiccups seem to be getting better with each new update, and that monitoring my phones behavior with each new relate might be the way to go. And since reinstalling the OS is a pain in my arse, I'll just wait for bug/behavior fixes.