Can't get it to compile because it's missing nzo_funcs
Looking at the exe the scroll seems to dissapear in places, that's pretty odd tbh the first things I'd test is to turn the black part of screen to pink or something to see if it's actually being drawn, secondly I'd be inclined to check things like the status of variables, for example how are you determining if the scroll is on back / front face? are there any instances where it could be neither?