Hi @sandum150,
I’ve just had a look at your source code, and I would say the issue you’re experiencing may be caused by the script caching and minification you’ve got going on there.
I would suggest deactivating all other plugins you’re using one at a time, starting with WP Rocket, and see if that restores the functionality.
If you do discover a conflict, I would suggest posting this on the NextGEN Gallery support forum, so the developers can be aware of the issue (this support forum is for the NextGEN Gallery Optimizer plugin, which you don’t appear to be using)…
https://www.ads-software.com/support/plugin/nextgen-gallery
I hope this helps!
Cheers,
Mark.