Missing Navigation Arrows

Hi

I uploaded a simple thumbnail gallery to my site, but when I click on an image and it opens up in a lightbox, there are no arrows left or right to move on to the next image. There is also no way to get out of the lightbox function other than to hit the back button on the browser. I am using the latest version of WordPress and my theme’s latest version (Salient).

Any ideas would be gratefully received. I can’t link up as it’s a private site for a client, but hopefully I’ve described the issue accurately.

Many thanks.