The documentation states that " When Datasmith detects multiple instances of the same block in your Rhino scene, it only creates one set of Static Mesh Assets for the geometry in that block. It then places multiple instances of those Static Meshes into the scene."
When I have been trying this, it creates a new static mesh for each object which creates significant slow downs on large scenes. Anyone have some advice on how to make this work?
In my experience, UE does make shared instances out of the objects inside block instances. You might have found a case where it does not export the block instances correctly though. I suggest making a simple scene with 2 instances of 1 new simple block definition to compare how UE imports that in your case. It might be that it does not work right for linked blocks or some other block features I have not tried yet.