I have just read that the new firmware version for the logger provides a new way to send the data using FTP.
I have a doubt. If there are a communication problem and that instant the logger has to send the data to the host, they are lost or however they are saved into the logger.
The data used is stored in the dataloggers normal data tables. The data is read out of that table and converted to the required format during the transfer to the remote ftp server. The logger holds pointers to the last data in the data table that it has successfully transfered. If the transmission fails those pointers are not updated so when the next transfer is attempted the datalogger will start reading from the same point in its datatables again.
You only risk losing data if the ftp server falsely acknowledges receipt of the data when it has not stored it correctly OR if the datalogger is storing data so fast it overwrites the data in its data table.