i wouldn't say rare nor would i say it's an epidemic when it comes to the crank hubs spinning. It's merely a design/engineering flaw that by the nature of the design is something that can definitely happen at any time.
However, i personally have not done research on this specific question, as i never had the urge, but maybe someone knows. Is the N54, N55, S55 interference or non interference engines. i would assume non, since i have seen people spin crank hubs. and simply reset the timing and drive on. If they are non, then honestly, i can kinda understand why they designed it that way, however, still should have been a solid or keyed part at a minimum IMO