If it's the magazine, easy fix, swap it out for another. It could also be the profile of the ammo, if the round nose hits the slide stop, that will cause it to lock open. I agree that it should be throated and polished, an easy operation if you know what you're doing. If it's a factory Colt magazine, throw it away and buy a Wilson.
I'd strip it down, and check out the bushing and the whole thing, the bushings on OMs are prone to breakage, which will tie things up, too. I'd bet seriously on the magazine, though, Colt used a cheap, bid-outsubcontractor's magazine.
The last thing, and I mean no disrespect, is called limp-wristing, which will also cause hangups. If the pistol isn't gripped solidly, the movement of the hands will not let the pistol work properly, as it has to have something to work against. All that takes to fix is a firm grip on the pistol.
I'd wager it was something simple like a bad magazine or grip, though, since Officer's ACPs are usually throated pretty well.