Default [Q] Screen Locking Automatically in middle of full screen games.

Hi, I recently got a tab pro 8.4, it's stock, not rooted. And like the topic saids, when ever i play games, it will randomly screen lock itself, even when my fingers are touching the screen. I would have to wake it up and unlock it again (and it takes longer than usually to wake it up when it sleeps like that), which pauses my games and makes most games unplayable (i tried 2 games, and it does the same thing.)

could it be a kitkat issue? or my tab is faulty? or just the games aren't updated enough to work with this tablet??? I'm kinda freaking out right now, thx.