In editor, custom primitive data dont work on instance static meshes in bp instance

Changes to custom primitive data properties for instanced meshes placed in the editor work in-game but are not otherwise reflected in-editor.

1. Create a BP actor with an instanced static mesh component.
2. Create a material with a float3 custom data parameter and connect it to the base color.
3. Set the material to the ISM component.
4. Add the actor to a level, and then change the custom primitive data value to a color different to the BP defaults.
5. Notice that the color change is not reflected in the editor, but it is reflected when in-game.