According to a number of user reports on Reddit and Google's own support forums, the latest Android 8.1 Oreo update launched by the search giant for the Pixel lineup late last year has introduced a new issue causing swiping gestures to misbehave on the lock screen. Specifically, users are reporting that swiping gestures are hardly being recognized when being performed on the lock screen, and this affects the user experience in various ways such as when answering phone calls, attempting to swipe away notifications, and so on. The problem doesn't seem to affect all users and a factory reset can reportedly solve it indefinitely.
The issue seems to affect both the first and second-generation Pixel smartphones so it's not specific to a particular model. Additionally, because only a relatively small number of users seem to have came across the bug, it may be that the problem is user-specific and might be triggered by external, i.e. third-party factors. Either way, some users have reported that they were able to bring their smartphones back to normal following the Android 8.1 Oreo update by factory-resetting their devices. This is, of course, a more extreme solution so not every affected user may be willing to go through with it before Google addresses the matter, but Google may eventually advise users to perform a factory reset anyway. According to users who came across the issue, swiping gestures are hardly recognized on the lock screen, with notifications requiring almost an edge-to-edge motion to be swiped away, and other users reporting that they were forced to swipe directly from the bottom to the top of the screen in order to answer a phone call.
Pixel owners running Android 8.1 Oreo and facing these problems can provide feedback to Google by navigating to their phone's main settings menu and heading to 'About phone' and 'Send feedback about this device' sections. Users can also visit Google's official support forums and provide feedback along with other users affected by the same issues. Keep in mind that the problem at hand seems to only affect Pixel devices running the latest Android 8.1 Oreo update which began rolling out in early December.