https://www.theverge.com/2017/10/22/16518298/google-investigating-pixel-2-xl-screen-burn-in

Over the weekend, people with review units of the Pixel 2 XL began noticing a problem. No, not the already-known issues of muddy color and grainy textures when viewed in low-light, but one that’s potentially more worrisome: screen burn-in. First reported on Twitter by Android Central’s Alex Dobie, multiple people have noticed that when you look at the screen with a gray background, you can see faint outlines of the phone’s navigation buttons on the bottom.

You can see it below, and I can confirm I’m seeing something similar on my own review unit.