It looks like fields are added through the rwmb_meta_boxes filter before the post request as been parsed. So $post is not initialized.
Is there a way to add or modify fields after $post has been parsed/loaded? E.g. to modify the std, options, value or description?
Since every code (incl. custom database queries or API calls) in rwmb_meta_boxes runs whether it is needed or not it can slow down the site. If we could conditionally add them based on e.g. the queried post_type, it would speed it up.