Google Pixel phone has drawn severe flak for its unreliable fingerprint scanner in recent times as several users have been complaining about its smaller surface area for registering finger imprints than the Nexus 6P, and an inferior sensor that's often buggy. Folks at Android Police have shared a couple of tricks to re-register the finger imprints in multiple attempts to fix this problem.
You could re-register the same fingers up to five times on the Pixel phone. The catch here is to change the angle or the position of the finger while re-registering its imprint on the scanner. You could vary the edge or side or even use the tip of the finger to register an imprint.
As you proceed registering the fringe areas around the finger pad, you will have the full imprint of your finger. Consequently, this technique will result in greater accuracy and reliability in unlocking your phone via the fingerprint scanner with less number of authorisation failures or rejected reads.
Alternatively, you can also try cleaning the q-tip surface of the scanner with little isopropyl alcohol and a microfiber cloth to ensure there are no smudges or dirt accumulated on the scanning surface.
[Source: Android Police]