3ds MAX MCG : Vertex Normal node returns NaNs?

Using MAX 2024, creating a tool that uses the “Mesh Vertex Normal” node. I will occasionally get {NaN, NaN, NaN} as a normal from this. in one test case about 5% of the normals are bad: 30,000 verts w/ over 1,000 normals all NaNs. The input is a SceneNode, not a mesh I’ve created in the MCG. I have made the simplest graph I can: A “Tool Input: SceneNode” into a “SceneNode Mesh” into the “Mesh Vertex Normal” node.

I cannot find any problems with the scene node/mesh outside the MCG. I have tried it as an Editable_Poly and and Editable_Mesh. I have collapsed the stack. I have thrown an Edit_Normals modifier on it - all normals are blue. I have inspected several of the specific MCG-NaN normals with MAXscript (Editable_Mesh: getNormal myNode , Editable_Poly: Edit_Normals modifier w/ ConvertVertexSelection) and there is nothing wrong, I get a correct unit-length normal back with MXS. Any other ideas?