Here’s a quick and dirty fix :
in /wp-content/plugins/wp-booking-system/include/pluginShortcode.php
line 10
replace
wp_enqueue_script('wpbs', WPBS_PATH . '/js/wpbs.min.js', array('jquery'));
by
wp_enqueue_script('wpbs', WPBS_PATH . '/js/wpbs.js', array('jquery'));
in /wp-content/plugins/wp-booking-system/js/wpbs.js
on line 87, add
var $instance = wpbs(this);
showLoader($instance);
//e.preventDefault();
if($instance.find(".wpbs-current-timestamp a").length == 0)
timestamp = $instance.find(".wpbs-current-timestamp").html();
else
timestamp = $instance.find(".wpbs-current-timestamp a").html()
wpbs_changeDay('refresh',timestamp, $instance);
Then clear your browser cache.