I get the same result as the above render. I imported it as a mesh, and instance it twice to apply my three multisub shaders for different color paint. I then deleted the old proxies from the forest list and added the new meshes.
Here is how they render on their own/instanced. Proxy on the left, imported as mesh on the right.
Note, this did happen to me before on my earlier tests with a different style of car, and I had to remove that one from the forest list. Otherwise everything rendered fine.