Faded out slide showing in the background

Hi all,

I'm using Storyline to create a 'form portal'. I've got an issue whereby one slide opens a lightbox slide, the lightbox slide then opens another lightbox, and the second lightbox slide closes when the user clicks a button and jumps to the 'Main Switchboard' slide;

However, this results in the below happening on the 'Main Switchboard' slide;

The first slide that generated the first of the two lightboxes is displayed behind the slide that the last lightbox has 'jumped to'. It doesn't show this up in the preview, but it does when published.

Anyone got any ideas and apologies if the above does not appear clear.

Cheers,
Cory