Reply To: By Post Field 'query args' with author

I think the problem is calling get_current_user_id too early. This docs page has an interesting comment:

Before the plugins_loaded action it returns 0.

So you might want to make some change to:

add_action( 'init', function() {
     add_filter( 'rwmb_meta_boxes', 'your_register_function' );
} );