Navigation Buttons Disappear After Using a Lightbox

I often lightbox slides via a Player tab, and I've never had that problem. 

Based on how it runs in Review, I'd guess that there are triggers to hide PREV and NEXT somewhere on the lightbox slide. But they are doing that on the main slide, not in the lightbox. 

• If there are triggers in the lightbox that hide PREV and NEXT, delete them.
• If you want to prevent PREV and NEXT from showing in the lightbox, be sure the "Use navigation controls" checkbox is not selected in the Player-Tab trigger.

If that's not the problem, I suggest you upload a copy of the .story file, because that will make it much easier for someone to troubleshoot. 

Here are the best practices for uploading a .story file:

• Only include slides that are involved in the problem.
• Be sure all objects, layers, motion paths, and variables have meaningful names.
• If there is proprietary content, replace or delete it. For example, replace proprietary text with ipsum lorem text.