I would recommend moving your obtain notifier VI's out of the sub-VI and outside of your main loop so that the notifier is only obtained once, and the reference is passed into the loop and into the sub-VI's
Look at the help for release notifier especially the underlined, bold, italic part.
You can use the Obtain Notifier function to obtain a reference to the same notifier with the same name multiple times. To destroy a notifier, call the Release Notifier function a number of times equal to the number of times you obtained a reference to the notifier or stop all VIs using the notifier reference.
If force destroy? is TRUE, this function releases all references to the notifier and destroys the notifier."
If it says you should call this function once for each time it is called, it must be building up numerous copies of this reference in memory. By slowing the loop from 1ms to 30ms, you are obtaining notifiers at 1/30th the rate, thus the program runs longer before bogging down the computer. Call it once (for each notifier) outside the loop, pass the references into the loop and into the sub-VI, I think the performance will improve. And of course make sure you use the release notifier in you main VI once your loop exits and the program is ready to end.
