The fingerprint sensor on my Pixel 9a has been fighting me since I got the phone. It really doesn't want to activate when I put the ol' digit on the sensor location. I have to push down and squiggle my finger a bit to get the thing to start up. But, once it does get going, it seems to work better than the one on the Pixel 6 did.
I worked around it by going to Settings > Display and turning on Screen Protector mode (even though I don't have a screen protector). Is anyone else having this problem with the 9a?