Won't display shader nodes anymore

Glad it worked out! Did you ever figure out what caused it?

I'm not sure I can explain it properly as I didn't completely understand what happened.
I realized that the gameobjects's materials using the shader had an incorrect path (something with "Hidden/..." instead of "Shader Forge/Flowmap"). I'm not sure why it changed to Hidden path nor why upon setting the path back to the proper path I finally was able to open it in Shader Forge. Why would a gameobject using the shader matter to the shader? not sure. I just don't know what happened ;)