IkariShinji, I can’t upload the file because it has an environmental texture from Substance Painter and it is 15 MB with it.
Parameters in the properties are as default, except for CPU that is now GPU and the samples are increased for the preview (nothing else has been altered). Plus: I am not using modifiers, and the material is only one.
The nodes in question are, as I said: Diffuse + Glossy in the Mix node, with some variations in the previews that you can see here (some textures applied; Fresnel applied; Bumps applied ecc).
The right-bottom preview is really only composed by colored Diffuse + Glossy (with roughness) into a Mix shader, going into the output node, and -nothing- else. Because of this, I thought that this was a very much common problem, since my settings are ultra-basic…
Burnin I can’t understand what are you suggesting… As I have said I have already added Fresnel in one of the 3 previews. (PS: I don’t want to use the Principled node because I want to learn how to use all behind it, before using it).