They're relatively new, they're relatively expensive (which saves them from being used in the worst of the applications) and like most things inherent to steel cable and whatnot they tend to get employed in situations where safety factors are generous. Don't count your chickens before they hatch.
You have a mechanical failure that can’t be seen in the labs and isn’t reproducible at other sites. Suggests something environmental.
Like when natural fiber army gear starts dissolving in the jungles of Vietnam.
Could be direct action, or a side effect of a chemical in plant or animal detritus. Like pigeon poop on car paint.
Active galvanic action will ruin your day.
I have a feeling such measurement and modelling might have been wrong.
It's easy to miss some oscillation mode, particularly high frequency longitudinal wave's in the cables, which couldn't be picked up by a laser survey due to the kilometers per second these waves travel.