Some time ago I could not enter my Samsung Galaxy S5 through the fingerprint reader, as when we do that configuration also asks us to load a password use that method to enter.
Next step was to look for something that I hint of how to solve this problem, but I did not find much, so I went to the scanning options and upon entering to register another finger to test if the service was active and I got an error saying "An error occurred with the fingerprint sensor. If this message appears repeatedly, restart the device. "
As the message says the reboot is a method that almost 95% of the problems solve on almost any platform, so without restarting the computer and everything returned to normal, the only good thing is that the S5 starts in less than 30 Seconds so you do not have to wait a long time, so for the moment that's the solution, at least until there's an update that will definitely end with this.