In fact it is not a bug: the vertex shader is fixed for particles, you can’t modify it, what you are editing in the NME is the particle fragment shader. The
Fog block has a vertex counter part that is missing when creating the particle shader, hence the crash.
Instead, you can implement the fog yourself in the particle shader, it’s not very complicated (I have implemented the EXP fog mode):
Note that I’m using a particle texture (
cloud.png) with an alpha channel and I set the blend mode to STANDARD, else you won’t get the effect you want (try changing the blend mode to something else and the texture by another one without an alpha channel like