I'm using MB with the Avada theme, and I only see "featured image" when I try to access any of the image elements from my field group. Is this happening due to incompatibility with Avada or do I have to install something extra in order to make this work?
It looks like the Avada theme does not support populating images from the custom field. You can try to contact Avada theme to ask for supporting this case.
Or use a tricky way, remove the post type support Thumbnail, then change the field ID single_image_asdf to this ID _thumbnail_id. You can still select the Featured image in the Avada dropdown but it will show the image of the custom field.