^^^This. Especailly the part about checking to see that the grip has not loosed up or moved. If you are not running spacers in STI mags, you will have issues from time to time. If the top round is sitting too low and thus getting caught under the ramp, you may need to widen the front of the feed lips so that the top round sticks up a little more. In the future I would suggest loading a little longer.
If you are not shooting major out of that gun your issue may be that the slide is not going back far enough. I know its sounds crazy that a 7 isn't letting the slide go all the way back but I have noticed that with 125 pf ammo, in my Limcat, that my MBX mags will do the same thing but STI mags run fine