I’m having the same issue. When I use Developer Tools and look at the Javascript console I see that the scripts are not loading due to a malformed url. It has lost a / between the .com and wp-content so I get this:
https://www.example.comwp-content/plugins/nextgen-gallery/products/phot…extgen/modules/nextgen_basic_templates/static/ngg_template_settings.min.js
This happens for all the Nextgen scripts.
