THE iOS 9.1 it was made available to everyone a few weeks ago, but it was only in the last few days that a problem supposedly brought about by him won out.
According to numerous reports on Apple's support forums, the Touch ID of iPhones became absurdly unstable after updating the operating system. Restarting the device, re-registering all fingerprints or even doing a complete restoration does not seem to help much or, if it does, it definitely does not help. Some users report slow identification, others say that they are now almost always required to enter their password.
Apple has so far not commented on the problem, but it is certainly already aware of it. Let's hope that a definitive correction comes in iOS 9.2, which reached its second beta this week. Remember that this is not the first, neither the second nor the third time that an iOS update causes problems related to the sensor.
Around here, I had no problem after iOS 9.1. Touch ID continues to work quickly and wonderfully, as I reported in my review of the iPhone 6s.