Hmm, I tried breaking my project, so I changed the cube hierarchy to the "incorrect" one, created a new meshlibrary, added the cube, removed the old meshlibrary from the gridmap and put in the new meshlibrary. The cubes would display in the editor but not in the game!
I had to delete the gridmap, delete the meshlibrary, create both anew and then I got the behaviour you are describing (visible just without interactions).
But once I updated the cube to have the "correct" hierarchy again and reloaded the cube from scene it behaved correctly again.
I have to agree with you that there is something really weird about the behaviour of this node, but I don't think I can determine how to fix your issue over the internet like this.
