Android 8.1 was a pretty minor update when it was released in early December, and while it added nice touches such as enabling the Pixel Visual Core and a new security patch, it also introduced a new bug that doesn't appear to have been fixed since it was discovered nearly a month ago.
On December 7, a thread was started on Google's support site titled "Android 8.1 Issues" with a user reporting that swiping up on the lock screen to enter their pin often doesn't work and requires them to swipe multiple times before it goes all the way up. Shortly after this, many other users responded with similar issues.
In addition to it being difficult to swipe up on the lock screen to go home or enter a PIN/password, it's also reported that it can often take multiple tries to swipe away a notification that's on the lock screen. This is something that I've been noticing on my Pixel 2, and I can confirm that it is extremely annoying to sometimes have to swipe three or four times just to dismiss a notification.
Along with issues on the lock screen, users have also noticed problems when trying to answer or decline phone calls. This is again something I've run into on the Pixel 2, and more times than not it requires multiple tries before the gesture is actually completed.
Based on Google's support site and Reddit, this is an issue that seems to be affecting both Pixel and Nexus devices running Android 8.1. We reached out to Google to see what's going on, but have so far only heard that the company is "looking into this." When we get a more detailed response, we'll be sure to let you know.
In the meantime, have you noticed any of these issues on your Pixel or Nexus phone?