This is a follow up to this post:
This is a similar problem. For some reason the translucent shader is not working properly in cycles:
Note, from left to right, it is Eevee, Cycles with the same light settings, and then Cycles with the point light turned down to 1W and no environment.
I have mixed translucency with the BSDF principled shader a more diffuse effect from the particles but it is acting a bit like a weak emitter. Also, you can see that the lens of the eye piece is emitting as well. There is no translucency set for that - it is just a simple image texture and principle BSDF shader. It ought to be completely in shadow.
For absolute sure, I am missing a simple setting somewhere. The Eevee version is what I ought to be seeing, but a little bit more realistically in cycles. What am I missing?
PS...I don't know if it is related, but Cycles is also ignoring the background when rendering. It is displaying a white background. (Blender 2.91.2)
Edit - I created a new blend file and appended the collection. I could not get the background to work properly in the original blend file. Once imported into the new blend file everything worked as expected. If any one knows if there might be seetting - I leave them to answer, otherwise the solution is to reconstruct the blend file.
Edit 2 - I have subsequently worked in the new file and attempted do use the same process. I added simple shaders to a low poly object, and in cycles it is not displaying the lighting correctly. The hat that I brought across IS displaying correctly. Again in Eevee, the new object (a boot) is displaying correctly. I cannot figure this out.