I don't think it's the ammo. Recoil didn't feel unusual, plus I was shooting my CZ75 with the same ammo and it shot fine.
The odd thing is I never get a stovepipe or any sort of missfeed. It's always the same exact symptom every shot. You'd think you get some shots that would extract more than others.
If the extractor was riding over the rim, wouldn't it chew the rim up as it came off and then rode back over again?
I'm not really seeing how a weak recoil spring could cause this. Wouldn't a weak spring still allow a shell ejection, but maybe cause a feed jam or something like that?
my expectation is it just isn't getting the case clear of the chamber
I'm thinking this is what is happening. Since I can't find anything else wrong, I'm back to thinking the rough chamber is slowing extraction enough to prevent the slide from coming back.