Yikes, not a big fan of that plugin – if you look at your error_log you’ll see why, it’s very buggy.
Is there a particular reason you use it over the default WordPress gallery?
WordPress gallery: https://codex.wordpress.org/The_WordPress_Gallery
Lightbox plugin: https://en-ca.wordpress.org/plugins/wp-featherlight/
Those two methods put together work really nicely for most projects I’ve seen.
Envira gallery is also worth checking out.
Let me know 🙂