Don't be too quick to discount operator error. 99 times out of 100, when things haven't worked out, we have only ourselves to blame. Not trying to make you feel bad, but in my own case, everything was sailing along just peachy, but every now and again, I would come off the strops in a funny way and cause just a tiny little bit of a rolled edge. It was always on the "dismount". I could do 100 perfect laps, and then screw up the very last one, and not even realize i had done it. Not suggesting that that is what you are doing, but don't discount the possibility that something is going wrong. I finally had to slow down, watch what I was doing and try to re-evaluate everything I was doing objectively. Try to step back and watch yourself critically for any deviation from a perfect stropping session.
Slow down and re-evalute, would be the pithy way to say it.