Black Squares in diffuse channel

[Robert]

I get that occasionally on scenes that one square in the image (its also sometimes just a rectangle) is pure black. Can't be a bucket. Any idea why this happen and what to do to avoid it?
Its really not happening often or in every scene. On a 300 frame animation I had it in 3 frames.
All rendered on Chaos Cloud.

[vladimir.nedev]

Can you show a screen shot of how it looks like exactly ?
Is it only the diffuse channel ? Not in any other render element or the beauty/RGB ?

It could be adaptive dome light or adaptive environment importance sampling (which is the same).
Do you have one of these two enabled ?
Recent nightly builds have a fix specifically for adaptive environment importance sampling, which might help, if you have that enabled.

Greetings,
Vladimir Nedev

[Robert]

Ok, I think it’s the environment hdr, it’s both in rgb channel and the diffuse output. Thanks, I get the new build and test again.. hope it’s for Modo too.