This is according to a post on the Google Product Forums (via Android and Me) where some users are complaining about the issue. The update to Android 7.1.2 is the cause of these problems, so if you have not updated yet, it would be better to delay the update. This problem cannot be solved neither by rebooting nor by formatting the phone. But, most importantly, some of the users are facing this issue, and not all the users.
"Wanted to let you know that we are looking into this issue with the fingerprint sensor not working after the 7.1.2 update".
New software updates are great for your phone - they patch security holes and bugs and add new features - except when they break a core feature, like your phone's fingerprint sensor. For now, it is highly suggested that owners of the Google Pixel, Pixel XL, Nexus 5X and Nexus 6P hold off on updating their devices.
Google is said to be aware of the Nexus 6P problems, with both the bootloop and early shutdown issues listed on the company's issue tracker but the issues bear with low priority tag and with no reported solution in sight. Did you manually flash the OTA update? Before that, Nexus 6P users were stuck to the unstable build of 7.1.2 where the other users were enjoying the stable build of 7.1.2. Now Google has rectified the situation and the stable release is being rolled out to users enrolled in the Beta program. It also brings back the Jio Wi-Fi VoLTE calling for Pixel users. Now Wi-Fi calling support has finally arrived for the pixel and Pixel XL via the 7.1.2 update. Where Wi-Fi calling differs from VoIP platforms such as Skype is the fact that whilst it also uses the Internet to make calls, they are placed with your mobile number and not via some external user ID.