This is a very strange one!!
I cannot see anything in the settings that would cause the extra image holder??
Sometimes in the interests of getting the project completed, it’s better to recreate than to spend endless time troubleshooting.
In this case you can copy and paste the ‘working’ lightbox link replacing the ‘extra image holder’ lightbox link.
- Copy the 1st ‘Lightbox Link Work’ element (including children)
- Delete the element ‘Lightbox Link’ (In the next 50 Column Center)
- Paste the copied ‘Lightbox Link Work’
- Replace the thumbnail image and the ‘Image’ element.
- Do for all Lightbox links with extra image holders
Hope that makes sense.
It’s not a fix, but a work around to get a publish ready site.
Let us know how you get on.