One temporary solution, which may or may not work for you, is to deactivate the always-on display feature. But then you’ll have to turn on the display to see the time and rely on the small LED light for notifications.
The June software update does, however, fix or improve a number of things. When connected via Wi-Fi or Bluetooth, you should experience better connections. Google also adjusted the proximity sensor on the Pixel 2 XL to be more accurate.
When the July software update hits in a few weeks, the bug should be taken care of. Google might be able to fix this by updating one of the Pixel-specific apps, but it does appear to be a system-level matter.
Article source: https://www.technobuffalo.com/2018/06/07/pixel-2-xl-wake-up-slow-bug/