hi there,
you can query that id in Account table. if you are using the ldap module for sync user, i think you can delete from account and import user again.
hope this help
See the release notes of Mx 8.6:
The message “Executing a query with an old implementation due to detected difference” is now a debug message instead of a warning.
So you can ignore this one or upgrade to Mx8.6+
Regards,
Ronald