First let me mention, that I'm not a mental ray expert, but most probably you'll need higher number of samples on those buckets.
I would suggest you a quick test using Forest Tools
and export all scattered geometry to instances. You can find it under Utilities
- More ...
- Forest Tools
. For more information about it, check our on-line reference guide
. This way you can check that the problem happens during Forest object conversion or not.
Also, please feel free to send us the simplified scene (containing problematic Forest object(s)) through WeTransfer
to email@example.com to analyse it here. Thanks in advance.