Hi,
Thanks for getting in touch. Chaos added support for ForestIvy leaves using our API. I can't find reference to it in their release notes to let you know the exact version, but from memory it was some time at the end of last year. For ForestIvy to work correctly correctly with Vantage, is is likely you would need to update it (and maybe VRay) to a more recent version. We just tested with Vantage 3 and it's working on our side.
Another option is to disable instancing in ForestIvy from the Display rollout, though obviously not as efficient, this should work with any version of Vantage.
I hope that helps, please let me know if I can do anything further.
Best,
Paul