As you may remember I had some problems with network rendering described here
I investigated the problem and here is the result.
When I was rendering the same scene over and over again with low anti-aliasing (1) I've got images where sunbeam artifacts were spread around terminator. I marked them with arrows. All these artifacts appeared randomly in each new render.
With anti-aliasing 4 the artfacts usually looked like this:
And the problem with netowrk rendering appeared because each render node was rendering its own artifacts. And because each render node is responsible for its own part of image these artifacts were cut somewhere.
For now I coped with the problem (by retouching the artifacts). But the main question is what are these artifacts and why they appear? I was playing with lots of settings: with GIs, samples, anti-aliasing, quality and details but nothing helped. These artifacts still appear in Cloud Layer v3 node (Low-level: Generic). Does anybody know what may cause this issue?