Yes, but it is on the ESP side, the ESP side see no errors, the FTP runs on a hosting service, all I can do is transfer files to it. There is no error anywhere in the process so the problem takes place but both the FTP and the ESP are quite happy that the process completed with no errors.
On the ESP side all I can check is if the connection with the FTP is still UP at the end of the file transmission and it is.
It does not help to, somehow, detect the error on the FTP side if I know of no way to communicating it back to the ESP for file retransmission.