I got the same problem, and I'm sure it's not a v-ray issue. I'm using max 2015 vray 3.2. And youre right Hadi the last F pack object is missingonly in the renders. I've noticed it flashes sometimes when i view it in wireframe mode.
Solution
This worked for me:
I've deleted the last f pack scatter created save the scene, close it and reopen max as administrator and rescattered the Fpack objects and voila!! it renders.
So I think it's a fpack issue.