Advanced permissions: Incomplete user/group list

I set up a groupfolder ‘foldername’ then I asigned an exisiting group ‘groupname’ to this folder, so that this group can write an share to the groupfolder ‘foldername’. When it comes to advanced permission a drop down list shows me some members of the group ‘groupname’ but only members til the letter ‘m’. Member names that begins with a letter after ‘m’ dosent show up. So only about the half of the group members get listed. Unfortunatelly the group administrators won’t show up either. I tried to change their names, but it didn’t help.

Is this a bug or something I can correct by configuration settings.

I’m ruinning Nextcloud 17.0.2 on a Debian 10 server (apache2.4, php7.3, mariadb).

Kind regards, go4ncloud