The Pixel 2 XL appears to have screen burn-in issues according to some users, who have been reporting that parts of the graphic on their screens have been visible even after backing out of those areas and moving to other apps. For the most part this seems to be popping up around the navigation bars, and it's worth pointing out that this isn't happening to all users who have the Pixel 2 XL, but it seems to be showing up for a fair amount of people who own the phone. That said, it's being reported that this isn't necessarily screen burn-in, and while it looks like that is indeed the problem it's not certain what the issue actually is at the moment, or what's causing it.
The potential burn-in isn't necessarily visible at all times, and it only seems to be the outline of the navigation buttons and not the entire button with all of the pixels from the area inside of the buttons. The report mentions that the burn-in seems to be showing up after at least a few hours of use, but also that it seemed to be on a consistent daily basis for those that it was popping up for. That said, it's recommended that if this is an issue that you're personally experiencing, you may want to sit and wait and watch to see if it continues, and then consider a warranty replacement or a return if it goes beyond a week or a month.
This particular issue may also very well be limited to just a smaller number of devices that from Google's early batch which means that it might not be a problem at all for future batches of the Pixel 2 XL. In addition to this issue, the Pixel 2 XL was perceived by some to have a more pale color on the screen, though Google was quick to comment and make a statement that said this wasn't a problem with the phone, but rather it was a result of trying to deliver a more accurate color reproduction for users. Screen burn-in probably isn't something that users with a OLED device are surprised by, as it's been an issue on other phones before. However, it's still unfortunate, so users should definitely keep an eye on their devices in the meantime.