Ok I got it working!
Problem was I set some parameters programmatically in said noise shader, and because I used 'tool' it did that already in the editor. When I saved the scene, this parameter was saved too, but couldn't be loaded, so it crashed.
That caused that it never loaded the scene, so of course I couldn't access the children nodes.
I deleted some lines in the scene file and got rid of the 'tool' term in the script. I can't see the shader in the editor that way, but at least it works.
