There are errors in the File Manager: cannot create files, cannot delete or move files and folders, cannot find the correct address of the folders, tested on 5 VPS servers with OS 6 and 7. This is only the webmin version. 1.930. If I go back to version 1.920 these problems disappear.
OS Centos 7
This is known and already fixed issue.
As a workaround, try switching to Authentic Theme.