Issue: In Skedler v3.12.x with ELK v6.6, Skedler generated PDF report sent to the admin email with at least one "no result found" visualization.
To resolve: In ELK v6.6 the error tag has been changed, therefore the tags(".visError" and ".kbnDocTable__error") need to be added in your $skedler_home > config > dashboard-tags.json file.
The attached screenshot is an example, which will help you to add tags at the right place.