A pistol can run like a champ for years, then suddenly starts acting up. You already ruled out mags and ammo, so that narrows things down. Yes, a worn extractor could cause failures to eject or stovepipes, especially if it's lost tension. Before swapping it, check the extractor spring too, sometimes that's the weak link...you can also take a close look at your recoil spring, if it's got a lot of rounds through it, it may be time to replace.
One more thing, make sure the chamber and feed ramp are spotless, even a little carbon or gunk can start trouble, especially if you're shooting different loads back to back.If it keeps acting up after those checks, I'd call Sig and see if they'll send an extractor kit or at least walk you through the next step. Their customer service has been good in my experience.