LDAP Sync works (no errors), but no users shown

[rsysadmin]

As you now have a useless Zammad installation, I would simply:
a) do a PostgreSQL backup of your Zammad database
b) ditch the current Zammad installation
c) reinstall from scratch

For c) you can use the installer script I release to the community a few weeks ago:

Zammad Installer script

HI all, I trust you are well. I like Zammad but found it rather tedious to copy & paste (or even type) commands, then jump to another page (i.e. to get Elasticsearch installed), then back to the original one, etc… you get the idea. I found some Ansible playbooks but they did not work as expected, so I decided to code a quick installer script for Zammad, a la old-school, to make my life easier and do the whole process in one go while I sit back and relax as the install process still requires s…

…provided that you don’t mind moving away from Debian to, say, Ubuntu 18.x or CentOS 8.

Otherwise, LDAP integration works flawlessly - we use it every day.

Please keep us posted!
PS - ich spreche Deutsch aber Englisch ist irgendwie die “Amtsprache” für Support