iPhone 6 starts acting weird after playing a game.

Hello.

I found that iPhone starts acting strangely after I play more or less hardware-intense game. Actually, the game I am playing is "The Room", but others like PvZ2 are also causing this. After launching and playing for some time (then quitting process) I get a random slowdowns and, more importantly, when I'm unlocking iPhone with the TouchID, I shortly click home button once and then just hold my finger on it without pressing. Instead of unlocking it ALWAYS shows up voice assistant. Also I noticed once that even without me touching the device it can pop-up voice assistance. I have original iOS 8.3 without JB or any weird software. Generally, my phone works fine unless I play any heavy-weighted game. Reboot will restore phone's perfect shape, of course.

Does that mean that iOS garbage collector does not work as intended? How can I force it to clear memory without reboot?