The way SC linkages work they get close to the inflexion point (if thats the right term?) at the end of the stroke. Perhaps the bottom-out bumper had failed allowing the shock to travel the small extra distance that allowed the link to flip over. Or potentially.. was the rider running offset bushes?
I was there and I fixed it.
Stato is right, the rocker rotated over center, so the shock is then forcing it in the wrong direction.
The bottom-out bumper is fine and the shock is the original correct one and was serviced/rebuilt after the first time it happened.
My gut feeling it that the frame/linkages/shock is right at the wrong end of the tolerances which allows a tiny amount too much travel.
The owner is contacting SC, in the meantime I’m going to add to the bottom-out bumper to stop it happening again.