There's your clue. That's probably because the slide isn't going back far enough for the slide lock to catch the cutout in the slide. What that means is, your ammo is a little on the weak side.Also, the slide didn't lock open when firing the last round in the mag.
No matter what the listed specs are for this 'cheap' ammo....its obviously a little too weak to run in your Q.
I'd say the aggravation is not worth the $1.00 savings per box.