What might cause this to happen? Maybe I pushed up on the slide release by accident? It is a stout load out of the M&P 9c, can really feel that slide moving fast, but it felt very controllable. I only had the one magazine so I couldn't run more Gold Dots to see if it happened again. It might just be a fluke but I didn't know if there was something I should check.
Other possibilities, although these are less likely, are 1) a slightly out-of-spec slide stop, or 2) slightly out-of-spec (too long OAL) ammo.
I've seen both in a couple of guns. In the case of the slide stop, check the tab where it is pressed up by the follower. If you see copper smudges on the slide stop, that might be it. This wouldn't necessarily be a problem with all ammo, but it could happen if the ammo is pushing the OAL range.
Check also that the ammo you're shooting isn't just a hair longer than usual.