I am trying to add the image caption after the featured image and I use the “post_thumbnail_html” filter. It works fine on single posts but does not work on pages. Basically can not modify the featured image at all with that filter on pages. When I disable the “GP Premium” plugin the “post_thumbnail_html” filter works again.
If the featured image size has been set in the Customizer > Layout > Blog – then GP switches that function – to get round that try the code i provide here: