There is a function simpleComputer.__add_related_ptrrecords(). The function constructs a wrong search filter: >>> search_filter = '(|(relativeDomainName=%s)(relativeDomainName=%s)(relativeDomainName=%s))' % (ip_split[0], '.'.join(ip_split[:1]), '.'.join(ip_split[:2])) → '(|(relativeDomainName=3)(relativeDomainName=3)(relativeDomainName=3.0))' This is easily fixed with: >>> '(|(relativeDomainName=%s)(relativeDomainName=%s)(relativeDomainName=%s))' % (ip_split[0], '.'.join(ip_split[:2]), '.'.join(ip_split[:3])) → '(|(relativeDomainName=3)(relativeDomainName=3.0)(relativeDomainName=3.0.10))' But the function seems to also called with the wrong zoneDN: It is called with the DN of the forward zone instead of the reverse zone. So it searches for pointer records underneath of a forward zone. And will therefore never find one!
This issue has been filled against UCS 4.1. The maintenance with bug and security fixes for UCS 4.1 has ended on 5st of April 2018. Customers still on UCS 4.1 are encouraged to update to UCS 4.3. Please contact your partner or Univention for any questions. If this issue still occurs in newer UCS versions, please use "Clone this bug" or simply reopen the issue. In this case please provide detailed information on how this issue is affecting you.