Unfortunately, I do not have access to Rehub RH code and that theme is not officially supported by Permalink Manager. Theoretically, you can try to force saving the custom permalink using extra code snippet:
function pm_set_custom_permalink( $data ) {
if ( ! empty( $data['post_id'] ) && is_numeric( $data['post_id'] ) ) {
$new_uri = Permalink_Manager_URI_Functions_Post::get_default_post_uri( $data['post_id'] );
Permalink_Manager_URI_Functions::save_single_uri( $data['post_id'], $new_uri, false, true );
}
}
add_action( 'wpfepp_form_actions', 'pm_set_custom_permalink', 999 );