Hey, thanks for the response!
The whole material of the plane was shown in first second of the video, it definitely does not contain any more nodes than was shown.
I tried to replace rock material by simple white material too – no effect.
I tried DistanceFieldGradient node, it had exactly the same artifacts too on every channel.
Plane has Affect Distance Field Lighting turned off and distance fields turned off, so it probably doesn’t do it to itself? But I’m not sure on this one.
Again, default cube works perfectly fine with the same material, but default plane doesn’t:
It’s still mystery to me.