I would suggest you to do a quick test using the Forest Tools
utility to 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, before rendering please remove all Forest Color
maps (if any is used) from your materials.
Let us know if there is any difference or not. Thanks in advance.