Is it possible you had a round with bullet setback that raised he pressures to do that? I just don't trust that powder, it's known to spike pressures when given the slightest reason to do so.
I still have 10 rounds of the 5.3grs and will take my calibers and check for setback this morning. No setback in 10 rounds probably will not prove a thing. it could be just that one case that was tired. I did pull the bullets on the next 5 rounds that was loaded. They go into the box in the order they come off the press. No I am not OCD, well maybe a little. The charges were right on and it took 2 hard wacks on my anvil to pull the bullet. The plating shower no sign of crimp imprinting so I could tighten the taper crimp up a little more.