This sounds like a software issue.
Try a hard reset. The process is a little odd on iPhone X since it doesn't have a home button - tutorial can be found here:
https://www.gottabemobile.com/how-to-force-restart-or-hard-reset-iphone-x/
If the hard reset doesn't do the trick, I'd try a restore (clean install) through iTunes. I'm using 11.2.1 on a 5S and have never experienced this issue, so maybe it's a bug unique to the X