Have you tried each barrel seperately. That can narrow the problem by 50%.
Appears to be firing pin drag which can be caused by overly long FP protrusion in some cases and by a hard edge on the firing pin at the edge of the radius. Sometimes you just need to break that edge of the transition from the major diameter of the pin to the radiuius and that may cure it. I would not shorten the pins, thats a last resort.

Brian
LTC, USA Ret.
NRA Patron Member
AHFGCA Life Member
USPSA Life Member