Pentax 6x7 (mlu)- blank frame

...the camera has given an unexposed frame half way through a film. I don't think it was operator error. Other online sources suggest failing battery (maybe silver oxide better than lithium) or some mechanical problem within the camera. Anyone here encountered this??
thanks.

Usually when you get an unexposed frame the mirror get stuck and you cannot shoot further without resetting the camera with a needle on the little black button (on right side of camera if memory is good, I don't have the camera with me while I'm writing). Failing battery or this problem have two things in common, you cannot operate the camera further,
So I think it's an operator error.