UCS destroying existing user & Group configs

brand new clean UCS install, but after connecting to a windows AD system, it syncs many of the items but fails to sync others , failing with errors.
After the errors the user/groups logins/details are corrupted on the master windows server, causing us to have to reenter/reset logins.

How can we track down the issues?

28.06.2020 13:54:15.577 LDAP (PROCESS): sync to ucs: [ user] [ add] uid=anna.smith,ou=procurement,ou=supply chain,ou=the office,dc=mirror-dn01,dc=org,dc=matel,dc=com
28.06.2020 13:54:19.885 LDAP (ERROR ): Unknown Exception during sync_to_ucs
28.06.2020 13:54:19.886 LDAP (ERROR ): Traceback (most recent call last):
File “/usr/lib/python2.7/dist-packages/univention/connector/init.py”, line 1326, in sync_to_ucs
result = self.add_in_ucs(property_type, object, module, position)
File “/usr/lib/python2.7/dist-packages/univention/connector/init.py”, line 1146, in add_in_ucs
return bool(ucs_object.create())
File “/usr/lib/python2.7/dist-packages/univention/admin/handlers/init.py”, line 557, in create
dn = self._create(response=response, serverctrls=serverctrls)
File “/usr/lib/python2.7/dist-packages/univention/admin/handlers/init.py”, line 1298, in _create
six.reraise(exc[0], exc[1], exc[2])
File “/usr/lib/python2.7/dist-packages/univention/admin/handlers/init.py”, line 1282, in _create
self.lo.add(self.dn, al, serverctrls=serverctrls, response=response)
File “/usr/lib/python2.7/dist-packages/univention/admin/uldap.py”, line 865, in add
raise univention.admin.uexceptions.ldapError(_err2str(msg), original_exception=msg)
ldapError: No such object