Backup symlink folder permissions wrong - pre 18.104.22.168
Any ISPConfig installation pre version 22.214.171.124 has the wrong permissions for the /var/backup folder, so the website smylink /backup folder does not work when users FTP into their site, getting permission denied when changing to /backup symlink folder.
Running this fixes the problem: chmod 755 /var/backup
Originally a pre 126.96.36.199 version was installed, where this was an issue. Then upgraded to 188.8.131.52, but this didnt fix the bug.