When testing access logging for FTP/SFTP/FTPS traffic in ProxySG, the transaction logged in the access logs is not seen while monitoring Statistics>Access Logging>Log Tail
Access Logging is not done until the end of a transaction, so it will not show up until the TCP session has ended.
For example, if using FileZilla, the session will not be completed until 'Disconnected from server' shows in the FileZilla log.
Please note that data connections may not end when the control connection is ended, it depends on how the particular client/server manage the connections. Wait until the sessions time out to see it in the access log. FileZilla will also display 'Disconnected from server' when a data connection is ended.