The door wont open when the shop is open but only when the shop is closed it will open.
bugs on DOOR
I don't really know how it happens or how to fix it, but it's been brought up before - Try constantly opening it and closing it and trying to get the sign to be in sync with it
Try sleep/save/quit and reload to see if it fixes itself. - maybe contact the other users on bug report megapost - and see what they were doing when it fixed itself.