It's really weird that this thread would pop up one day before I had the very same problem with some of my AN470AD4-5 rivets. I squeezed about a dozen of these today and nearly every one had a 45 degree crack around the outside of the shop head.
Here's a photo:
They really acted like they were especially hard. Before I found the problem, I remember thinking it was odd how my pneumatic squeezer hesitated for 1/4 second or so after clamping on the rivet, but before it actually squeezed it.
I also had driven a few of these with the gun today. Here's a close up of one done with the gun. Notice how the sides are very bumpy and there appear to be some voids in the end face of the rivet.
In contrast, here is one done with the gun today, but from a differnt batch. The sides of the shop head are much smoother and there don't appear to be any voids in the end face of the rivet.
I had two more compartments full of this sized rivet in my storage container, so I just discarded all the ones in the compartment I had been working out of.