The affected Pixel 4 users reported about the issue on multiple platforms. And when users try to erase existing facial data, according to reports, they see an error message "Unable to verify face". Once the Pixel 4 was launched, users discovered that face unlock had one critical flaw when compared to Apple's, as it didn't have a Require Attention option - that someone could unlock your phone by holding it against your face while you sleep. Among the supported devices were only Google Pixel 3, Google Pixel 3 XL, Google Pixel 3a, Google Pixel 4 and Google Pixel 4 XL, plus Chrome OS-based tablets. You should still protect your handset with a password, even if face unlock fails, and you should definitely install all the security updates that Google releases, even if you risk running into unexpected issues like the face unlock bug.
For some users, they abruptly started receiving system notifications asking them to re-register their face again, despite the face unlock functioning fine. It indicates that the face could not be verified, inviting them to try again. However, it is also occurring without getting the update. But, if the user removes or re-add their face data to fix the problem then also the issue is not being solved.
Fixes, like deleting face data and reconfiguring face unlock; and restarting the Pixel 4 in safe mode, don't work. So, for all those who are affected by this problem in their device they can do a factory reset, even though it always does not fix the problem. If you do do the factory reset, make sure to take a complete backup of your device first.