My moto g2 power key z just loosely when I unboxed it ..
Is it a factory problem .
yeah.. got my moto g 2 today, have the issue as yours . Searched the internet for this and it is too common. Guess they are all that way , no need to worry about.
I just got my Moto G 2nd Gen last week and the volume & power buttons are both loose/wobbly. Seems to be common on Motorola phones.