Hello Scott,
The iteration input is just a way to optimize your code. What happens is, if the iteration input is greater than 0, then LabVIEW does not call the config VI everytime, as it knows that it has already configured the port. If it had to call the config port, it will result in overhead. I did look through the snippet of code and it looks pretty straight forward. So you might have to start looking at other avenues that might be causing the issue.
-Arun V