The hook looks a little off...but it could just be the pic....is the hook rounded just a little bit?
It should be straight and flat....if its not that could cause it to slip over the rim as the slide comes back if the pressure hasn't fully dropped when the slide starts moving (the timing on a 36 doesn't leave much room for error)
Check the rim on the round it leaves in the chamber....you should be able to tell of the hook has been dragged back over it.
A new extractor is about $20...Or Glock would replace it for free if they can replicate the malfunction.
My 36 has NEVER missed a beat, and I've tried every conceivable scenario to make it choke (limp wrist, mixed ammo in the mag, etc...even all of them combined)...it just keeps on going like the energizer bunny (several thousand rounds so far). The only quirk I've noticed is erractic ejection with weak ammo (such as WWB)...it still runs even with that, but it throws brass in all directions.