I have several ldap user directories in Confluence similar to below.
ou=UsersA,ou=example,ou=com (users and groups appear in Confluence, groups are populated)
ou=UsersB,ou=example,ou=com (users and groups appear in Confluence, groups are populated)
ou=Groups,ou=example,ou=com (has a group containing all users in UsersA and UsersB)
This final group is empty in confluence
