I just noticed that WinSCP using FTPS Passive mode, is causing serious issues on our FTP server (FileZilla server 1.2.0)
Something goes wrong when closing the TCP socket for a PASV connection. All PASV ports on our server are in a TIME_WAIT state.
Eventually our server runs out of available PASV ports, and WinSCP can't download files anymore, until these TIME_WAIT states expire.
Tested this with FileZilla client, and no issues occurred. Same with CoffeeCup Free FTP, so the problem is definitely caused by WinSCP.
Please fix this.