trees disappearing - animation

[MQ4267]

hello, so the twist is, i'm using max 2017 with IRAY+ (plugin for 3ds max from nvidia).

i'm doing an animation with a camera in the air, moving, trees in the background scattered with the latest version of forestpro.  ok, at first it was a lot of trees disappearing, but then i turned off the limit to camera view.  a lot more objects, 23.9K objects according to forest lister, all trees. but it still renders, except that witin the first 40 frames of the animation, 2 or 3 trees will suddenly disappear and not come back.  it seems random.  i've got a "dense map" 800'.0 units (not xy).

my camera far clipping plane is 20,000 feet, back offset 20 feet, i'm using distance falloff, min 0 ft. max 10000 ft.  "limit to visibility" is un-checked so not sure of that far clipping plane is working or not, it does not seem to be

thank.

[MQ4267]

i believe i solved the issue.  i did in fact have to turn off the density fall-off.  next time i will try to do a different curve, that does not affect trees so "close" to the camera.