I watched both videos and it looks to me that on the return stroke the razor digs in the leather probably from the heavy wrist movement.
I used to do the same thing but i learned to strop without moving my wrist and its definately an improvement.I hold the razor between my thumb and index finger at the tang and both finger flip the razor the scales rest inside my hand my pinkie actually helps the flipping as well hard to describe.
Another thing i notice is both of you hold the razor with the thumb on top of the tang and that will cause the wrist movement, there is no way to flip the razor without moving the wrist with the thumb on top of the tang.