The tag "v0.9.3" points to an unstable release of v0.9.3.
git clone https://github.com/NodeBB/NodeBB.git cd NodeBB git checkout v0.9.3
results in a commit hash da78e4f... one revision before this issue was fixed.
I had to
git reset --hard 6486197623f8f32ab354503ca40ab6e8e3e4551e
on a fresh checkout to get the same stable "v0.9.3" hash , I got on another machine by first checking out v0.9.2 and then upgrading to v0.9.3.
No issues with Mongo 3.2.1 with this "v0.9.3" revision.