Sometimes, when you open the Visual Portfolio popup gallery, it displayed correctly, but some of your site elements (especially site header/navigation) are displayed above it.
To fix it, you just need to add custom CSS with z-index fix:
body .vp-pswp,
body .vp-fancybox {
--vp-popup__z-index: 9000;
}If this will not help, try to use value bigger than 9000.