Apple has admitted that there are issues with the screen on the iPhone X in a suitably downplayed support document called ‘About the Super Retina display on your iPhone X’.
Here’s what they have to say: If you look at an OLED display off-angle, you might notice slight shifts in color and hue. This is a characteristic of OLED and is normal behavior. With extended long-term use, OLED displays can also show slight visual changes. This is also expected behavior and can include ‘image persistence’ or ‘burn-in,’ where the display shows a faint remnant of an image even after a new image appears on the screen”.