My second shadow 2 developed the same problem at 3-4000 rounds. It would run fine for about 150-175 rounds and then FTE. Did it to me 3 times on one stage in a match. I tried removing the extractor and cleaning it and the channel - didn't help. Then I replaced the extractor spring with a new oem spring - didn't help. Then i replaced the extractor and spring - didn't help. Then I replaced the oem extractor spring with the extra power spring with 1-1/2 coils cut off and haven't had a FTE in 750 rounds.
I'm Mikiem's friend. The problem occurs on the last round of the mag. When the last round is stripped from the mag, the trigger doesn't reset. Hit the mag release and it will reset. As mike said, I am left handed and switched the mag release to be lefty friendly.