Jmeter OS Process Sampler

I'm using 4 OS Process Samplers in Jmeter to launch binaries. Can't really say much more than that.

When I run the test, the first OS Sampler doesn't work. And by that, I mean it doesn't fail or succeed, it just takes too long. Nothing happens. When I stop the test, the error is that it failed because it got interrupted (by me).

When I run the test a 2nd time, the first OS Sampler works right away, but then the same problem happens with the 2nd OS Sampler.

On the third test try, OS Sampler 1 and 2 work quickly, but the 3rd one doesn't.

On the fourth test try, OS Samplers 1, 2, and 3 work, but not the 4th.

Finally, on the fifth test try, all OS Samplers work.

So all in all, each Sampler needs a trial run before it works.

Why? Please help.