A specific disabled user account is causing the Active Directory sync to fail.

- Account: W3Guest3
- Error: 2019-06-12 21:39:16,419 Caesium-1-4 ERROR ServiceRunner [c.atlassian.scheduler.JobRunnerResponse] Unable to synchronise directory
java.lang.IllegalStateException: User 'W3Guest3' has no unique key mapping.
During troubleshooting, we enabled the user account; We were then able perform a full user directory sync.
- When disabling W3Guest3 again, we get the same error message.
- This account shows as disabled in the JIRA database like all the other accounts:

Confluence has no issue with this user account. It actually doesn't appear in the AD/Internal directories with the Confluence database.
Suggestions?
Thanks,
Jonathan