If the firewall is open for port 990 why would FTPS fail to return the contents of a file? The query goes out to the server with no errors logged. Get creates the file on the client side but the file is empty of content. Read write permissions are set on the folder. Thank you in advance.
Since FTP(S) uses at least one secondary port for data connections, one or more additional ports have to be opened in the firewall.
So a good solution is to define a limited (and constant) port range for all FTP data connections and open these ports in your firewall. Typically you can define these ports in the FTP server configuration.