I just got an iPhone 6 and the auto lock feature is not working. I went to General Settings and set it up so that it auto locks after one minute. It doesn't "lock" however. After one minute the screen turns black, but to reawaken the phone, all I have to do is press the round key at the bottom -- it doesn't prompt me for my fingerprint or passcode. Is there something else I need to turn on? I already set it up to read my thumb print earlier.