Overlay reappears after closing opt-in

I installed a pop-up opt-in. After I close it by clicking the (X) and scroll down the page a bit, the overlay reappears again. Kindly have a look and see whether this is an incompatibility issue with another plugin (although I had tested this by disabling all plugins, without success). Or, could it be an incompatibility with my theme (Enfold)? I have given you support access.