The gray meshes are caused by the Material not enabling its usage for Instanced Static Meshes. Normally, if you apply a material to a mesh in the editor (or in sub editors, including the components view), Unreal will just handle setting that material’s usage to match what you’ve put it on (like applying a material to a particle system will enable usage with particle sprites).
doesn’t seem to be happening here. I’m guessing that it’s because there’s no actual instance of the mesh on any of the Instanced Static Mesh components till the game is running, and it doesn’t update the material in the running game.
Just any material you want to apply to these components, go into the material editor, select the material node (the one you wire everything into) and in the Details Panel scroll down to Usage, and Enable “Used with Instanced Static Meshes”