It survived 5 Minutes of riding, than fractured.
due to bad planning (material for a recess could not be removed because it was too thin) the washers were too thin. So the pressure rested on the printed part instead of the washers.
I suspect while tightening the hub screw it already suffered the critical failure. Then the chain tension while riding gave it the rest.
The too thin recess is fixed in the next version and extra support was added where it broke.