Without seeing the details of the settings, mesh and textures it is almost impossible to answer this.
It could be that the twist is putting two surfaces (front and back ) at the same location. A big no-no in 3D, and in real life, but one which Photoshop does not have the tools to resolve.
Can you post a link to the actual file that we can take a look at?
Thanks for your quick answer, Dave!
I just made it again and you can get the PSD at https://adobe.ly/2GOY07O
Nothing fancy there: I created a rectangular path (100x5 pixels), extruded, twisted and applied the 'Plastic Acrylic' texture. Then again with a 100x1 pixels path (the one failing).
What I fail to understand is that, even if the two surface were messed up, the "mesh" itself shouldn't be shown. A distorted shape would be more likely, no?
Anyway... I hope there's a way to correct that or, at least, go around it and create the desired shape with some kind of magic trick
I took a look at the file in Photoshop then in Blender. The issue is with the mesh geometry in that the extreme twist on the very thin cross section is causing the faces of the mesh to cross each other i.e. a front face is crossing the back. That can't hap[pen in real life and causes the ray tracing to go awry.
Your choices are :
a. Increase the thickness
b. Reduce the twist
c. Make the mesh in a proper 3D programme where you have control of the number of faces and can prevent the cross over
I still find it weird that the mesh becomes visible, though, instead of just distorting the shape (mathematically speaking, because to the eye it looks fine), which I would have guessed would happen if the faces crossed each other.
In any case, it seems I unfortunately won't be able to do what I had planned, at least not only in Photoshop. I'll install Blender and give it a try ASAP.
Thanks again for your time!
If the mesh was made of smaller faces then it probably twist without them crossing. Unfortunately the larger pieces introduce that cross when twisted.
If you install Blender, export the scene from Photoshop as *.obj then import it to Blender, put the model in Edit mode and select a front and back face. By orbiting the view around it you will see immediately what I mean