I love the Google Pixel, but there's no doubt that in the last few weeks I've noticed its fingerprint scanner becoming less and less reliable (I've heard it from others, too). I was puzzled, as the whole idea behind Google's Pixel Imprint is to become more accurate over time as it gets more and more reads of your finger. I tried removing my fingerprints and re-adding them, but that didn't help at all. So I went back to an old trick I used on some of the first touch-to-scan fingerprint reader phones - registering the same fingers more than once.
I know, I know - there's a limit of five total allowed on the Pixel, and this isn't exactly the most scientific workaround. But here's the thing: it works. To prevent the Pixel from thinking you're trying to register the same finger again, start with an odd angle on the finger you want to re-register, like the edge/side or the very tip, and then register all the fringe areas around your finger pad, but avoid the "typical" placement with the pad squarely on the reader. I found this helped with both of my index fingers, and especially the one I use to unlock less frequently (the left one). I actually registered my left index finger three times without issue, and the number of rejected reads I'm getting has been dramatically reduced.
It's a bit annoying that this even works, but it was starting to really drive me a bit crazy lately how often my Pixel would fail to read my finger. In the 48 hours since I've done this, I've had maybe two or three rejected reads, and all of them because my fingers were wet. Give it a try - I can't guarantee this will work for everyone, but my results have been great so far.