Hey, thanks for reporting! This took a while to investigate but found the problem:
The reason your model wasn't loading was a combination of an internal bug with the shader (as you correctly found out) but also because your file includes spaces on the empty lines. Asset Forge didn't like this and refused to load the model. In the new version which is releasing soon (preview-1c) I've fixed these bugs and it'll load even with the extra spaces. I've also fixed the issue with GLTF, the filename is now correct.