Idk why the conditions inside request and wp_headers always retuned false I was unable to determine the request. I ended up with some similiar solution. But thanks anyway!

Page is not accessible outside of our network so I don't care about search engines. Anyway... the whole upgrade marathon started when the wordpress cannot upload new files. As soon as I moved some old files manually the upload was working in that moment. So I think the server has its own limitations.

Thanks for this tip! Although it strips out the href link on first save on post. It is necessary to save and then again edit the image and set the href target again.

This solution is fine except since WP 4.5 taxonomies should be passed via the ‘taxonomy’ argument in the $args array. $taxonomy = get_terms(array('taxonomy' => $term, 'hide_empty' => false));

I have no idea how to achieve that with unserialize.. Also I have doubts about the LIKE method :-/ I'm still PHP beginner.