We are using the shortcode in a custom field, rather than in the body of a page. This prevents the validation script from being enqueued, because the function is checking to see if the shortcode is being used in the page content.
I have modified your plugin code to use this method of enqueuing the validation script. Would you be able to include this modification in the next version of your plugin? I’m happy to provide the code updates. Let me know if I can help.