If a Cubmap is not marked as readable shaderforge will crash and corrupt the shader file making you lose all your progress.

In order to reproduce it create a cubemap via asset > create > legacy > cube map. Do not mark the cubemap as readable.

Go to shader forge and create a new unlit shader with a cubemap assigned to custom light.

Go back to unity, assign the shader to a material, assign the cubemap, now try to open the shader via the button "Open shader with shaderforge". The window will be empty and a lot of error will pop in the output. And what's worst, the shader code will be corrupted and wiped to an "new shader" template,