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

Assume you have this code to register your meta box:

add_filter( 'rwmb_meta_boxes', 'prefix_register_meta_boxes' );
function prefix_register_meta_boxes( $meta_boxes ) {
    $meta_boxes[] = array(
        // Your meta box code goes here
    );
}

Then change it to:

add_action( 'init', function() {
     add_filter( 'rwmb_meta_boxes', 'prefix_register_meta_boxes' );
} );
function prefix_register_meta_boxes( $meta_boxes ) {
    $meta_boxes[] = array(
        // Your meta box code goes here
    );
}