I raised a JIRA support Issue See https://support.atlassian.com/servicedesk/customer/portal/22/JSP-262974 and they suggest to contact you
After upgrading the "Email This Issue" several exceptions thrown
Find attached the JIRA_support log. The upgrade of the add-on was done in atlassian-jira.log.2.
Also attached an (outlook) mail from Atlassian regarding this Issue
Thanks for your help.