I've been experiencing random restarts here and there since the Lollipop update. The phone freezes then restarts and when the home screen comes back up it says "Android updating" then it performs like normal and I'll get a error report screen .
When the error report pops-up for you doesn't it has something like view more details?It says unknown reset just saying it reset for some reason do u wanna report yes or no
So it is rebooting into safe mode, have you installed any app/game from outside the PlayStore? If yes, uninstall it and see if the issue will reoccurre or not.