https://support.atlassian.com/jira/kb/an-unknown-exception-occured-executing-validator-comatlassianjiraworkflowskippablevalidator/
An unknown exception occured executing Validator com.atlassian.jira.workflow.SkippableValidator |...
Learn how to resolve the Jira cloning issue caused by the SkippableValidator error when attachments are involved.
atlassian jiraunknownexceptionexecuting