Since December Security update I have an issue with the fingerprint unlock. Sometimes my fingerprints aren't recognized.
When I delete a saved fingerprint and I try to save it again my phone tells me that the finger is wet or sensor is dirty. I cleaned the both and I tried again. The result was the same.
I've encountered what you had experience and what I did was press the power button harder and hold it in while fiddling about with my finger (move fingers about the power button while keeping it held) to get register back sometimes. It is frustrating but it works.
On mine, I find that it is more sensitive to unlocking when my finger is hitting the button more towards the top of the button. When I say the top of the button I mean towards the actual top of the phone where the headphone jack is. Smash it more up in that direction. If I let it hit more towards the bottom of the button it doesn't work as well. Thus another reason for my vote to have it moved to the back!
