Checking around the community, certain shaders tend to have conflicts with fog effects, specially with PP mixed. First that comes to mind, it could be an issue with your material’s blend location, which establishes at what point of rendering is the toon shader applied.
To test this out, open your PP toon shader mat, navigate to details, and look for the post process material section. Open the drop down menu for “Blendable Location”, and experiment with each setting. Before translucency settings should ensure that the shader is applied to the character before the volumetric fog, and after translucency will do the opposite.
