I and several other Xs owners have noted a slight stutter in scrolling and the app-closing animation after a period of inactivity. For example, if you have the screen on with an app open and just leave it alone for 10 seconds, then either start scrolling or swipe up to close the app, there's a slight stutter in the animation. It only does this after a period of inactivity, and not if you're actively scrolling and using it. 

I (and a lot of other people) have reported this to Apple. They ran a test and said that there was nothing wrong. We want Apple to take this problem serious and fixes the stuttergate or let us return the iPhone. Please help us!