It can happen that a corrupt file in the server directory causes a display error in the user administration. Most of the time this then manifests itself by the absence of all users in one / several locations / configuration groups in the admin interface. The users themselves do not notice this and can continue to work correctly.
Solution for this is the following:
1. stop the XPhone Connect Server service
2. navigate to the path C:\Programs\C4B\XPhone Connect Server\MailServer\Settings
3. back up the contents of the Settings folder and then delete it
4. perform a repair installation of Connect Server and then start it again