DC Promo not working after lost primary DC

My Primary DC is lost (broken, no good backup) and the Backup DC cannot perform “Backup 2 Master” steps because of missing LDAP connection…
PS: Maybe, the ldap connection problems is quite old (weeks).

I am willing to build a new DC and to promote the current Backup DC. But, performing
/usr/share/univention-samba4/scripts/purge_s4_computer.py --computername=v723ucs
on the Backup DC (primary DC was named v723ucs) returns the LDAP error:
authentication error: {'desc': "Can't contact LDAP server", 'errno': 107, 'info': 'Transport endpoint is not connected'}


  • The UDM (https://<backup-dc>/univention/management/) is also not working fully as all LDAP relevant tasks (aka almost everything) are timing out. Login as such is working well.
  • (Non-UCS-) LDAP-connections from other hosts work. Backup UCS is responding, users can login for example to Nextcloud (one of the “other” non-UCS server)

How can I solve the LDAP Problem?
What is the way to remove the link to the non-working old Primary DC?