I guessing that you are left handed, leaving 7 pins. That being the case and you made the normal moves with your game and equipment that should help,..I'll turn to the lanes...several things can cause the 7 pin for a LH, or 10 pin for a RH...
1.) you may have been on a pair that had "bad racks", pins being off spot ever so slightly can cause what should be a strike, to be a corner pin. any of the front pins on your strike side side can cause this...
2.) If the lane and the pin decks are not flush with each other the ball can actually get airborne as it enters the pocket area, losing all it torque and drive, hence deflection...this is hard to see if the lane is higher, not so hard if it's the pin deck because the ball will hop slightly,..look at your track for little nicks where it may have been hitting the raised pin deck...
3.) todays lane dressing machines have a mind of their own,..sometimes. The machine may have malfunctioned and put oil further down the lane than normal, or the stripping function may not have worked, causing the ball to never pick up a good roll and hit...
hopefully this was a one time event...remember the pair of lanes that this happened and watch for these tell-tail signs on that pair next time,...if it continues I would get someone with bowling knowledge to look at what you're doing,..maybe they can spot the problem....
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je
