Hi! As we’ve already discussed in other support threads, and as it’s stated in the plugin’s description, not all themes are compatible by default with our plugin. There’s more than one possible way to include a featured image, but we can only hook (and thus manipulate) one of them.
In order to fix the issue, we need access to the source code of the theme. Please, send us a copy of your theme (customers AT neliosoftware DOT com) and we’ll look into it. Also, it’d be helpful if you could please share a couple of links to your website: one with a regular featured image (which should work) and one with an external featured image (which, as you’re reporting, shouldn’t).
Thanks!