I had this with a cheapo cam and was told it was the lens. Took the cam apart & fixed it firmly with epoxy & all sorted.
I later had the same problem with my DOD cam, when I took this one apart, I noticed the lens was screwed down but the screws pressed on springs which, in turn, held the lens down. I tightened the screws ever so slightly & the problems was fixed.
Is it normal for you guys?
It does it other times when not as hot.