Sidebars Pro not working properly and displaying error

I've recently moved this site over to the Pantheon servers (it's not live yet, the above link is for development only). I discovered that there is an error message for my custom sidebars in the widget manager.
Missing argument 2 for apply_filter(), called in .../class-custom-sidebars-visibility.php on line 531 and defined in /srv/.../wp-includes/plugin.php on line 177
Any idea.