Another thing I noticed is that for all of your revs you are pretty much up the back up the ball which depending on the pattern could cause early burn with no grab on the backend. Do you have any other releases?
If at all possible could you bowl an entire game, with the camera looking down lane in slow motion, and don't change anything with your hand? I think it has more to do with hitting your breakpoint consistently.
Even when you hit the board you intend to get the ball out to, it isn't guaranteed that you threw it to the same spot, because you could be getting the ball to the 4 board at 40 feet one time, and to the 4 board at 42 or 38 feet the next time. A suggestion to fix this is to get the last lane in your house, put two pieces of tape on the on both sides of your intended breakpoint creating a gate. You can make it wide at first to get used to it, but you should slowly move the pieces of tape closer and closer together till your breakpoint is a 2 board gate.
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