Dark buckets in rendering

[davision]

I have a flame rendered against a window.

Some of the buckets are coming out strangely dark. It is not just the glass but also the window frame that darkens. I think it's related to reflection but don't know what's going on.

The buckets that are dark are random from one frame to the next. I have the flame being rendered inside a gizmo so I don't think there is any intersection issues with the glass.

Any ideas?

[Ivaylo Katev]

do you use distributed rendering?

[davision]

No. I agree it looks like a distributed rendering error but no, definitely did not use that here. It was a normal backburner job with a about 6 different servers.

[Ivaylo Katev]

is it the same when render without backburner?

[davision]

Yes. The problem remains. But interestingly it's not the same buckets that are dark each time. I rendered the same frame twice on my workstation and the dark square pattern was different.

There is a car model reflected (and near) the window. If I hide that, the problem seems to go away. But I have no clue why that affects it.

[Ivaylo Katev]

can you send us the scene for investigation?