Apple has determined that some iPhone X displays may experience touch issues due to a component that might fail on the display module. An affected device may exhibit the following:
The display, or part of the display, does not respond or responds intermittently to touch
The display reacts even though it was not touched
Apple or an Apple Authorized Service Provider will replace the display module on eligible devices, free of charge.
No other iPhone models are part of this program… More here.
I have see this happen on mine for a while, usually at the far edges of the screen. I didn’t think much of it, but guess it will need a trip to the Apple store to fix.