lightbox navigation

Hi,
I have a problem using the navigation arrows in lightbox. I can’t click on them and they switch very quick in the top corner of the screen and if i click, it closes the popup.

You can check it out here: http://www.s-bauhaus.ro/en_GB/pictures/

Hope you can help me.
Best regards.

https://wordpress.org/plugins/wp-ultimate-gallery/

Later Edit: It’s theme related, i will try to investigate my theme.