It is the gallery overlay (
nivo-lightbox-overlay) that is blocking everything else on the page. You can find it just before the body tag closes. If you inspect its CSS after closing the lightbox, you will see that its
z-index is very high.. and it does not matter that the
opacity is 0, it will still obstruct your other stuff as long as it’s not
display: none; or
z-index: -1; or whatever suitable.