LDAP User import from Univention LDAP directory

I try to import user to GW 18.5 and 24.1 from an Univention LDAP directory. But I get always the message "Users to import into GroupWise: 0" in the preview.

The LDAP server / directory is configured and works (context browse works). LDAP trace on Univention shows the query and also that users found (GW search for objectclass=inetOrgPerson).

The Univention directory works with "uid" as primary attribute (eDir use cn).

Is there an logfile on the GW server where I can see why the import doesn't work or what is the criteria for the import process to decide "this is a user..." ?

Any ideas ?