This problem having now been experienced by Grockle and Chris 99 shows that these parts have a lower than required mechanical strength and even if the bolt had come loose the anti rotation features in the pulley should not have broken out
These faults and the appearance of the new items (including the camshaft pulleys) would indicate that they have been produced by a powdered matallurgy process such as sintering.
Given the small diameter of the anti rotation features in the crankshaft pulley, and the resulting high loads at this point, these pulleys (if not also the camshaft pulleys) should really have been machined from solid steel and not sintered.
