JIRA Agile tab is missing from the instance

The JIRA Agile appears to be disabled. Under the JIRA Agile add-on if you try to enable it, you hit into error:

This add-on failed to enable. It may require a license. Refer to the logs for more information.

The current workaround is to restart the instance. If you are raising an issue, under https://support.atlassian.com, do let us know the best time to restart your instance.