When Confluence attempts to synchronize from an external directory and hits a duplicate that exists in the external directory-- like a user who is in two OUs that are within the scope of the filter. The remaining users in the directory are not Synchronized and instead just reported:
The directory synchronization is halted leaving all other users without issues out of the synchronization. This can result in new users not being synchronized to the directory because one user exists in two locations in the source LDAP directory.
Skip the duplicate user and allow remaining users that are not violating any constraints to be synchronized so that the impact of a duplicate in the source directory is lowered.
Per our Confluence does not complete directory synchronization when a user is duplicated in multiple OUs article, remove the duplicate user or adjust the scope of the LDAP search exclude the duplicate.