The issue seems to have start between V-Ray Core 5.10.03 and V-Ray Core 5.10.20.
Here I use the latest ACES 1.2 from GitHub - colour-science/OpenColorIO-Configs: Color Configurations for OpenColorIO · GitHub
and as you can see that since V-Ray Core 5.10.20 banding artifacts started to appear
houdini 18.5.499
linux centos, cinnamon
to the left is:
V-Ray for Houdini number:12523 hash:fba7db2 from 25 May 2021 02:03 (build number:12523)
V-Ray Core 5.10.03 from 19 May 2021
to the right is:
V-Ray for Houdini number:14462 hash:8cd7621 from 05 Aug 2021 02:02 (build number:14462)
V-Ray Core 5.10.20 from 2 Aug 2021
Dear LeoYfver, hello.
We are investigating some banding issues when low-intensity lights are used, so you are right on time.
It will be very helpful to share the lighting setup or a test scene, that you have used.
That way I will perform the very same test - for now I am not able to reproduce such a clear difference.
Thank you in advance.
Best regards,
TS
here is the file. Btw as a sidenote the scene crashes often when either moving or pressing a button in the VFB.
Regards Alexis
banding.zip (1.49 MB)
Thеn 2 in 1 for looking at.
Thank you!
I am also seeing this issue in some renders using the scattering shader.
Happy to announce that the described from LeoYfver banding is handled in nightlies.
Please check the latest (from today).
I have just tested it both on win & linux and could confirm.
Dubbie99, please give the mentioned build a try.
If you are still experiencing it, we will need more information and run more tests.
Thank you both.
Wishing you happy Friday the 13th.
@tsvetomira.girginova thank you 
will will probably try it next week.
and happy friday 13th to you too 
