Its more than likely the result of road vibrations/body movement, combined with the forces from the downforce the wing creates

It seems to me that on the roadsters, the wing is very long (front to rear) and putting that huge surface on the end of long standoffs only increases the torque effect it has on its mounting points (torque = force x distance) I would say that a fix would be fabricating aluminum standoff brackets for the wing.

Initial investment might be a little on the high side but it would still be cheaper than buying and painting new wings left and right