Alright, lets say first, I admire your determination to make this work.. It's looking great already.
Now some things I noticed;
1) there should be a global admin who can put all race joiners on ready. Or disable(/enable) the ready option to be initiated by any client. The absence of this functionality is frequently a problem during league organizing also.
2) You say it only happens on motherboard2, right? Motherboard1 never goes black? Then what is the difference between the two, thats what I would question myself
3) What happens, just for test, if you not F11 all screens and just keep it windowed for the sake of testing. Does it still goes black? Do you see the window borders? What happens if you make the window active? What happens if you move the window around on the assigned screen?
4) .. I have no 4 yet.