The screenshot i've added this message will help you anderstand what the problem is : i have strange artefacts on a cyc
at first i thought it was a Normals problem but as you see, point normals and prim normals point inward, in right direction.
The render looks weird as if there was sort of a problem with resolving geometry which is a grid with a bend.
And it's not GI light related as i've changed my lights for native Octane ones and problem still persists.
May be this is just a very simple newbie stuff, i don't know what to look for to resolve this !
thank you for your help !