I think I'm having this same issue on a render I'm trying to do currently, relative to another thread here...

I'm pretty sure I've tried everything suggested here correctly, I think, apart from maybe adding an AO node... I'm rendering IDL. Although have tried rendering with IDL off and just an infinite light... but getting the same thing with the artifacts.

I've tried adding an AO node in the following renders... but I plugged it into the specular colour... which I'm thinking is not correct?

Where about in the nodes for the material should I be plugging in the AO node?

Here's a couple of pics of what I'm getting... darker polygon artifacts visible in the ships sails:

(can I somehow upload and embed images here by the way, rather than just add a link to my external urls?)

Firstly using the vendor supplied jpg texture based material for the sails. This material is just two nodes. The default and a colour image node. There are black / shadow polygon artifacts on the sails still (and that strip along the horizon line, that I think is just from me plugging in the AO node in the wrong place):

I've then tried replacing the "canvas" material for the ship's sails with a basic procedural shader too, using a 3d clouds node instead of the jpg texture in the Colour image node. I seem to have managed to invert the lighting of the artifacts (towards white instead of black as it were, through my general lack of shader ability, LOL) but otherwise, the polygons are still visible on the sails:

Thanks :-)