Now, i could be completely full of it....But I did an exchange today for a different phone and this scanner works way better. Also notice that the home button has a different feedback when pressed.
My other S6's scanner was not terrible. But it would be temperamental sometimes for reasons I could not understand. Like my finger would definitely be in a prime position and no other factors like wetness etc and it would just refuse it. My new phone works perfectly and is much faster with the scanner. So if you can't get it to work for ya, might want to consider a swap as the last resort