Weird.. Tweak A or, B don't cause issue like this... Try something.. Go to setting-device-display-display time-out Change the value to 1min. - exit from setting and don't touch your phone 1-2min... If still no lock, try this again with another value.. If still not work, shut down your phone, wait 2-3 min. and switch on.. Don't touch your phone until it completely loaded.. Just wait until it lock your screen..