You are adding this image from Enfold theme image element, right?
This could be the issue.
if the theme builder is storing the image as URL then may be WPML media can not replace it.
In order to help you better I need to debug this issue locally, for this I'll need to temporarily install a plugin called "Duplicator" on your site. This will allow me to create a copy of your site and your content.
Once the problem is resolved I will delete the local site.
I hope this okay?