But you’re not going in circles – Or shouldn’t 🙂
AdRotate outputs that code. Either via Shortcode or PHP snippet.
If the plugin you use to share the posts to Facebook does not exclude that code (usually shortcodes) that’s a problem with that sharing plugin. Nothing I can do about that.
So if they have no clue, or won’t help. Find another sharing plugin. Jetpacks sharing module works fine for example.
The code outputted is related to Caching, setting up caching properly may help too, but then it logically would include a working advert instead of the code that should show the advert. So the problem then (again) is with the sharing plugin for not excluding it.