I own Moto X 2nd gen. and it goes into priority mode automatically. It is very annoying because the priority mode switches of my WiFi and reduces the phones ringtone volume.
About phone (click the image for its larger variant)
Uninstall Battery Doctor
I figured out why this is happening. It's the Battery Doctor which turns off my Wifi and put my phone in priority mode.
I tested 3-4 times, when I enable (start) Battery Doctor, the issue was reproduced and when I forcefully stopped it, phone works properly.