http://www.techradar.com/news/pixel-2-xl-screen-burn-in-problems

Reports of Google Pixel 2 XL screen burn-in problems are beginning to mount, less than a week after the new Android Oreo smartphone went on sale.

Screen burn-in occurs when the same image stays on the display long enough and a ghost image remains, even when moving to another screen. That seems to be what's happening on one of our Pixel 2 XL phones and those of other reviewers who have had the device in hand for about two weeks.