Why does app execution pause when a script is getting data from DAQ

I have a script file which collects data from a DAQ. The script calls an App (GUI) which essentially just serves as a front end for interaction and data display. There is a while loop with a pause() in the script to control timing (sample rate). I understand that I can drop all the code in the app, however I am trying to avoid renaming a bunch of variables. Anyway, I have a non-interruptible button whose callback modifies an App property. Now the weird bit. If I am not reading from the DAQ and instead have a dummy function generating data, the button callback executes perfectly. When I replace the dummy function with the DAQ single scan the callback never executes, but ends up in the queue and executes when I force quit the script. Can someone explain this behavior? I can easily circumvent the problem with a state button, but I want to understand why it is happening. Specifically, why the DAQ call is preventing app callbacks from running.