I dont know if this is the best palce to post this, but I'm having the same problem described on the first message.
Really slow times when creating a second forest objet in max 2016, and slower with the third one and so on.... the first one works just fine, its created the way it has always been...(quick and nice)
The difference with NL2911 problem is that in my case it happens with just a plane as ground and three teapots as scattered objects (one for each forest object)
I detect that my problems is worst when the ground object is bigger (its slower in a 500 meters ground than in another of just 20 meters)... but is alaways slowing down when creating new forest objects.
Also, when I used vray proxys that where created in max 2014 (99% of them where created in max 2014) some times, max crashes.
Thanks in advance and sorry if this wasnt the place to post this.