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.

Post update, restart the Skedler service and you're all set.
However, this manual effort will be automated in our upcoming release Skedler Reports v4.0.