The plugin: plug_eventbooking_cartupdate.zip is the same as plug_eventbooking_acymailing.zip in the install package. So after installing this on your joomla site cart update does not work!
Actually, in our latest version, we don't need that plugin anymore (the code of that plugin is moved to Events Booking - System (DO NOT UNPUBLISH) already
So maybe you can uninstall that plugin and test everything again to make sure it is working as expected