just had the same problem with LG G3. I figured it out. lock the screen (using the button on ur phone that locks the phone). the screen should fade to black, like it normally would when u lock ur phobe.then, with the screen black and without having pushed anything else on the screen or the side of the phone, 'Knock' your password on the screen. Your phone should unlock!!! Hope it works!! important to note tho: how u normally unlock the phone will not work with knock unlock and TalkBack activated at the same time. the only way to do it is as described above: lock the phone so the screen goes black, then just tap ur knock password right on the black screen. it will unlock it phone immediately, but be careful because TalkBack is still activated and it is very annoying navigating with it turned on. good luck!