Having a similar issue but it seems only to be effected with Smooth enabled for displacement up to level 3
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The file is downloaded, you can remove it now.
There is a issue grass object in your scene, which does not have any face on this object, and it cause Iray crash when processing its material.
Team will try to avoid this crash happened, if you want to work on this project, please try to delete the issue grass first!
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