Very easy fix
Load up your window and expand it right. Full quit button functionality returns.
Your Number of Players and Max Players Allowed labels and corresponding number labels go over too far like Valaury hinted at with the DZ_LeaderValue. Your R and T buttons are indeed rendered after your leader labels, so they worked fine. Your Players labels were being rendered last and as they extend to overlap the Quit button at the default size, this was preventing the left half from being used.
As far as fixing the window, you have two options.
Option 1: Resize the labels to a smaller horizontal size. This will remove the overlap.
Option 2: Move those 4 <Pieces> up higher than your <Pieces>DZ_Quit</Pieces> ... this will render the Quit button after the Labels and allow for full functionality
Option 1 is a fix, Option 2 is a bandaid. Both will serve your purpose.