The with class fluid-row in which you have the lightbox has "visible-desktop" class. This hides the whole div when you decrease the window size. Since the parent div display is now none - all the children (including the lightbox) are hidden. This happens because you have non unique ids in your HTML. id of the element should be unique - you have the same div id="demoLightbox" multiple times. So it picks the first one.
Create separate div ids for each of the versions (desktop, table, phone).