shrunk lock screen, although screen lock is switched off at all

My LG G2 mini randomly comes to some shrunk lock screen as attached screenshot, not allowing me to use my phone at all, must to press Volume down key plenty of times to get the phone unlocked. I even set None screen lock at all, anyway it comes to this terrible lock position.
Any ideas to resolve this glitch? Btw, master reset hasn't helped, as well as upgrading from KitKat to Lollipop.

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shrunk lock screen, although screen lock is switched off at all