The problem was experienced first time today. We manage to redo the relink by manually going to the element and then select image.
After a few access to the editor to edit/remove/re-add this problematic 13th element, i was looking at the scenes on the left side, and as i press(select) the scene, it goes from populated with the images it contain, and suddenly it goes white. Upon checking, it looks like the development environment lost links to all images.
Fortunately all the image entry elements names are same as actual file name.
So far so good, after manually relinking images.
Really cant find any explanation in the behaviour above ( opacity refuse to kick in).