Images open in seperate page and not in lighbox

Hi there
I’ve been using this plugin on a few sites and it has always worked perfectly. But on this site (https://www.birkenheadpub.com/gallery/), it doesn’t want to work and just opens the gallery images in a separate page all together.
Would appreciate it if someone could give me some advise.
As far as I know there aren’t any conflicting plugins.
Thanks
T

https://www.ads-software.com/plugins/lightbox-gallery/