A yard or anybody would assume that a boat that has a keel is meant to be blocked up under its keel and steadied by jacks along the hull sides.
As long as the blocks are placed evenly, and the jacks just snug, no damage should happen.
I have seen fiberglass boats with incredibly flimsy hulls, where placement of blocking/jacks was very tricky, hope yours isn’t one of those!
Do you have any pictures of the boat on it’s blocking?
Surely you did bottom paint while it was on the hard, was damage not noted then?
That might point to damage during or even after the launch.
You can lead a horse to water,
But you can't make him ski...