I read the other threads about the empty folder issue in OMV. My situation is slightly different: using the built-in FTP client in windows (i.e. typing the address in Explorer) leads to show the actual content of the FTP folders.
Instead using other applications like FileZilla or ES File Explorer (Android) leads to a correct login but they show nothing in the folder.
May I assume at least the permissions are ok? Otherwise even Windows should not be able to access the files.
I attach the proftpd.conf file.