I have a Samsung Galaxy S4 (GT-I9505) with Android Lollipop (5.0.1), and rarely, my pincode just fails to accept when I'm unlocking it. I pick up my phone after not using it for a few hours, enter the pincode exactly like I usually enter it, but it disappears and I get the error "invalid pincode". I try 5 times in a row, keep getting the error and end up getting locked out for 30 seconds. I've had this situation twice so far.
The only way I found to fix it is by rebooting my phone, which means I lose everything that's not saved properly. Obviously this is pretty annoying. Are there apps that can hijack my unlock screen like that? If so, how do I find such apps? Or is there another reason for this?