A lot of reverse pivot happens with one plane swingers. Are you a one plane swinger?

It can be induced by the rotary movement of the shoulders at the start of a one plane swing i.e. the left shoulder rotates down and under the chin which forces your whole upper body turn toward the ground and you tilt rather than turn into your right side. This leaves varying proportions of weight (depending on the quality of the turn) on your left foot = reverse pivot.

As a suggestion, try thinking of moving your left shoulder straight across to your chin, rather than down and under in your backswing.

Might help.