If it was the Pixel 6, I can attest that the 6 (at least the 6 Pro XL) had issues with the fingerprint scanner. I had no issues with my 5 series (when the fingerprint scanner was on the back) but the 6 series always gave me trouble. I'd wager a guess the reason why was because it was the first generation with an under-display fingerprint scanner and they hadn't yet worked out the quirks.

I've since upgraded to a 9 series and it works flawlessly so I can assume they've figured it out some time since then.