Nextcloud 14: New Users/Groups do not appear in combobox if i try to share a folder

Dear All, this is the issue I face in Nextcloud 14.0.3:

Nextcloud version : 14.0.3
Operating system and version : Ubuntu 16.04
Apache or nginx version : nginx (Ubuntu/Plesk)
PHP version : 7.2.17

The following issue appears:
I added new users and/or new groups. After that I created a new folder and wanted to share this with the users. In the combobox of the share configuration the new users and/or groups are not found/displayed. (but older users/groups found/displayed)

Is this the first time you’ve seen this error? (Y/N) : Y

Steps to replicate it:

  1. Create new user and/or group
  2. try to share folder or file with new user/group

How can i resolve this problem?