Ok, after fiddling around with debugging and testing things, I believe I have solved it. So my thought process was the user inputs an IP Address 220.127.116.11 and before closing the popup numberpad, clicks on the different LineEdits to change the IP Mask 18.104.22.168. That is why I was checking if(num->isVisible()) because then it would close/delete/popup each time a LineEdit is clicked. I was having problems/segmentation faults because after the user clicks "Done" (or presses Enter/Return on the keyboard), the popup is deleted so checking isVisible()) resulted in errors.
To fix this, I created a boolean value numVis that is true if the numberpad is visible, and false otherwise. It is this value that I am now checking and everything seems to work just fine. I hope this makes sense.
I will go ahead and mark this as solved.