Ok, weird. I tried now and I get the same effect you talk about when I don't check unbound scrolling. Everything is moved to the left on the iPhoneX but as soon as I check unbound scrolling it covers the whole screen and is perfectly centered on all my phones including the iPhoneX.
So for me that solves the issue.
The iPhone X has another aspect ratio than other iPhones so that is why it looks fine on most iPhones except iPhoneX if you don't check unbound scrolling.