(10-23-2019, 08:44 AM)Toni Santa Wrote: It seems the connection was closed by the server with "426 Data connection closed abnormally"
There is no way to diagnose this with just the client's log. All the client knows is that the server reported an error had occurred, but it does not know what the error actually was.
On the TIdFTPServer side, a 426 response is sent if an uncaught exception is raised. Either when building the directory list itself, or if the TCP connection used for the data transfer can't be established, or if there is an error negotiating an SSL/TLS handshake for the TCP connection, or there is an error transmitting the list over the TCP connection, etc.
The only way to know for sure what is actually going on is to debug your server when the error happens.
However, I will say that I don't see any data transfer related security commands in your log, such as PROT. You say your server is secure, but the client is not trying to secure the transfer of data. How exactly do you have your TIdFTPServer configured? What are the actual property settings?