Could it be like a lock pick process where you start from the left and see if you get further or can throw away that guess, so by having the "choices" be at the beginning you don't have to make them again and again? (and for whatever reason doesn't/can't cache the prefix)? Or could it be like when counting

     100000000000
     010000000000
     110000000000
     001000000000

most of the variation is at the left and you only rarely see changes at the right? Would be interesting to get this answer from from someone who knows hashcat and isn't just pulling answers out of the air like me :)