Are you running Redhat? There was a RH version in the 7s, I've forgotten which one, which changed something that required everyone to up their stack size. I currently have "expr 1024*1034" for the main stacksize (in ns/parameters) and "expr 512*1024" in the per-thread stacksize.
I'd try this even if you're not on Redhat, because the result of a too-small stacksize is exactly what you describe, sudden and immediate nsd death.
