I faced a weird problem where the model I download from SketchFab was having some texturing issue and did not respond as expected to lighting.
Where the model should have looked something like this.
This was my Material Setup where I created a Master Material with Default Textures and used different instances for the parts of the model.
If you are facing the same or a similar issue please make sure you have changed this in the Material
This seems to fix a issue and hope it saves your time.