I had the same problem with missing leaves, although i didn't notice it at first because i had no referrence how they should appear and i thought "this is it" π
Annyhow i don't use Lumion anymore due to it's lack of realism i was looking for. Now that I purchased the full Maxwell Studio license i can use the Xfrog models withouth any workarounds and also using instancing it is quite nice perfomancewise.