During a current project I got this artefacts. I use progressive GPU rendering at VfR. I found it helps to switch from GTR to Phong. Is it a known issue?
-Micha
Such a nice bug and no response? I hope the team is well.
Hello, Micha,
There are a couple of unresolved bugs which produce identical artefacts.
Could you please confirm whether disabling the Adaptive Lights checkbox in Render Parameters > Optimizations fixes the problem for you?
If not, please share the part of the scene you’ve used to illustrate the issue or let us know if the problematic material can be found in one of the scenes you’ve already shared with the Support team.
Thank you!
I tested my project scene again and the bug is gone. It seems to be fixed by the last update. 
If I see the issue again I will do your recommended test.
Thank you,
Micha
Hi @Peter.Chaushev ,
I got the artefacts again, but the workaround works. I sent an example file → 302-043-5792
Good luck,
Micha
I have exactly the same problem. I can confirm that turning off adaptive lights solves the issue but of course, rendering is now slower.
Finally I found that some spot lights caused the issue. I moved them down from the ceiling and the error was gone. Also I found that the shadow radius influenced the aretfacts. Maybe it was a problem that the light radius intersected the geometry.