I’ve had trouble with these mags before and it was caused by a broken wire where the small plate crimps the harness to the mag plate. As the mag plate advances, all the flex is in this area compounding the problem.
I don’t have the manual in front of me giving the specs for the two coils but if you hook up an ohmmeter to the coils leads and slowly flex the wire harness, any jump or variation in the reading will confirm a break in the wiring. It’s also a good time to confirm the coils conditions to as they can go bad.