My 0.02, coming from personal experience and observations:
Had erratic extraction on Shadow - works 100% for a couple of range trips, works not but stovepipeing alot.
Pulled extractor out. I drove extractor pin from top of the slide down, not all the way but till extractor fell out, with spring. Spring was weakish, and worn on outside of coils, made me think it was larger than needed in overal diameter and was binding/getting stuck due to much friction. New +25% spring (from czcustom) was installed, gun failed chambering test - spring was longer than factory and got fully compressed on installation, it could not compress anymore, extractor would not pivit. Pin, extractor and spring are back out, spring is cut to match factory lengh, all installed back. All tests went fine.
I also used nail polishing emery board to polish extractor's top and bottom surfaces, cleaned cavity in slide and claw as much as I could (they were clean, actually). Also, thou gun was bought brand new, I was surprized to see extractor being 'three dot' one.