Using WordPress Gallery

I am trying to add a simple wordpress gallery to a page on one of my sites. I can only get the images to display if I disable the override functions in misc settings – but this means the gallery doesn’t function properly – so I can see the images but when I click on them I can’t exit out or scroll to the next one.
See here: https://www.thecakehouseuk.com/gallery-test/

I have tested this on another site of mine which is also using virtue and I can successfully add a wordpress gallery that works like it should (as on the demo page) https://themes.kadencethemes.com/virtue/wordpress-gallery/

Why is it not working on the other site? I can’t see any plugins that are reacting adversely with it. Help please!

many thanks

Nic