My guess is something binding on the horizontal plunger which prevents it from retracting all the way past the catch that holds the eyes open or binding in the vertical plunger to prevent it from returning to closed position after the horizontal fires to release.

I just recently completely rebuilt Red in my Roadshow (same mechs) with new coils, new plungers, new nylon eyelets and springs. I kept messing around with it but it was working inconsistently. Between a stronger spring, smoother plungers, smoother coil sleeves, smoother eye action due to new nylons and less slop from wear in the whole operation it now works every time rather than inconsistently. May have been overkill, but I was tired of messing with it and it didn't appear to have been rebuilt ever (or at least in quite some time).