ajax-action.php can’t find added action

You can’t hook an AJAX action from within a shortcode, and the constructor for Wp_Lbs_Calendar is only running inside your shortcode.

This means that the actions are only hooked to wp_ajax_ when your shortcode is used on the page. But the AJAX request is a separate request to admin-ajax.php, and your shortcode is not running on on that page, so the actions are not hooked and will not run.

Your add_action()s for AJAX need to be hooked in a place that lets them run on every page load, so that the handler is available on admin-ajax.php.