The factory crank hub bites with the crank end basically by a friction disc design. It holds tightly most of the time.
When the RPM changes, there will be shear force applied to the disc. The scale of the force is correlated to parameters like engine load, RPM, torque, etc.
So in relative short terms, if there is huge variation of engine rpm under full load, say a downshift when the engine is accelerating full boost, the hub will see the most disadvantageous situation. The shear force may exceed the holding capacity for the friction discs, causing the separation of hub&crank, hence the faulty valves.
In long term situation, the factor of fatigue seems to be more of the concern. If the car is frequently tracked, the friction disc may wear, and eventually lose grab like old clutches.
But I have seen no experiment with all the variables strictly controlled so above is more or less my speculation. The only solution for now seems to be swap out the factory hub with pinned/one piece ones, as long as no friction discs exist for this part.