Correct me if I'm wrong, but I believe you're talking about the bottom side of the firing pin Channel that rubs on the next round in the magazine.
That area should always be stoned and Polished to a mirror finish. If not done just causes a lot of resistance to the slide, and in this case enough resistance that the slide does not lock up properly.
I was referring to the breech face (should have said so) but I did also lightly break the sharp edge on the front & rear of that bar that runs along the bottom side of the firing pin channel as it was leaving a slight line on the next round in the magazine. I did the rear corner also to allow a smoother hammer cock during recoil (I usually do this on all my CZ's) I just hadn't got around to doing this one yet.
We'll see what happens when I get out on my range tomorrow as I would like to confirm improvement.
I have other shooting commitments that come first so those have priority.
