Unfortunately, the search giant did it again, as Android 7.1.2 Nougat update breaks the fingerprint sensor on the Pixel and Nexus smartphones. For the time being, it's unclear if this is a widespread issue or something isolated.
In any case, Google must replicate the bug before trying to find a solution. Luckily, there are many Pixel and Nexus users who have taken it to the user community forums to complain (and explain) that their fingerprint sensors are not working any longer after upgrading to Android 7.1.2 Nougat.
Even after they have deleted all the fingerprints stored on the phone and did a hard reset, the fingerprint sensors on the affected Nexus and Pixel handsets refused to start working again.
At the moment, the issue affects both the Pixel and Pixel XL smartphones, as well as the Nexus 5X and Nexus 6P. The cause of the problem hasn't been identified yet, and there's no workaround to make the fingerprint sensor work again.