I faced two problems using Forest Pro with scattered, animated vray proxies:
First: After rendering the material of the scattered proxies looks different than the one of the source proxy. Hereby it does not matter if I assign a material (the same material) in the Forest Pro Rollout under "Geometry->Material" or not. The result is the same. Somehow it looks much lighter and each grass blade got its own "Tint". I do not use Forest Color for tinting, so I can't see why the blades are nevertheless tinted. The material assigned only uses Multi/Subobject(1 Slot)<-VRayMaterial<-Bitmap(Diffuse). I attached an image with an example. To the right you can see the source proxy, to the left a bunch of scattered proxies.
Second (my main problem): While rendering an animation sequence with this setup the material suddenly changes in frame 38/39. Most of the light blades get dark and vice versa. First it looked like some of the geometry disappers, but the blades only get very dark. The source proxy nearby looks good. The color doesn't change. As expected. I attached three frames (37-39) which show the color jump of the scattered proxies, while the source proxy doesnt change.
The scene is useless in this state. I have no clue what is going on here.
System: 3ds Max 2018, Forest Pro 5.4.1., vray 3.6