Spark plug electrode bending

This girl my cousin works with has a 2008 Charger expolice car 5.7 94000 miles on it. First off I don't know the girl or the car. She had a misfire on cyl. 6 guy she took it to found that the spark plug electrode was bent on one of the spark plugs. Not bent down to hit the center electrode but bent at the end where it connects to the threads and then follows the profile of the center electrode up. So they replaced all the spark plugs. Ran great ... for a day and then it started to act up again this time on number three hole one spark plug did the same thing. Neither one of the times did there appear to be any contact with the piston. Bore scope did not show any marking on the top of either piston, and the electrodes didn't show any signs either. I haven't seen it first hand. I'll see the plugs for my self tomarow. Does any body have any ideas?
Author: exhausting