Delayed notifications are one of the most enduring issues with Google Pixel phones, and Google seems to be aware of the issue.
I’ll have issues after taking a screenshot and navigating back - I just get a non-responsive black screen sometimes except for the navigation buttons. Those are partially unresponsive, and I have to tap them chaotically to get rid of the black screen.
I think the whole Android system navigation has been broken since Google started rolling it into the Pixel Launcher.