IPhone 6 turns off?

I own an iPhone 6 that is in good condition. Only I have a problem there, and every time I'm on a particular app I have to hold my phone to the side but every time I hold it with this app, my phone turns off by itself. It appears a black screen and the small rotating wheel and after a few seconds my phone goes back to, so it does not turn off completely. But this happens somehow only in this particular app so if I hold my phone, for example sideways if kch on Netflix am nothing but why?

Which app does that happen?

At a game

Uninstall and reinstall the game.