winscp连接阿里云，总是提示重新连接

winscp 官方说法:
Host is not communicating for more than 15 seconds. Still waiting... Warning: Aborting this operation will close connection!
主机通信时间超过15秒。还在等待...警告：中止此操作将关闭连接！关闭优化连接缓冲大小
You get this message when WinSCP is waiting for response from the server for more than configured time. Note that this is not an error message, WinSCP still keeps waiting. If the server responds finally, the message goes away automatically. The message box is shown only to give you a chance to break the connection and reconnect, if you do not want to wait anymore.
当WinSCP等待来自服务器的响应超过配置的时间，您会收到此消息。请注意，这不是错误消息，WinSCP仍在等待。如果服务器最终响应，则消息会自动消失。如果您不想再等待，则会显示消息框，以便您有机会断开连接并重新连接。
If the server never replies, it may be because of some fatal error on the server side. Also something may be interfering with the connection, preventing the server response from arriving or possibly even the original request to arrive at the server.

如果服务器从不回复，可能是因为服务器端出现了一些致命错误。还有一些东西可能会干扰连接，阻止服务器响应到达或甚至可能是原始请求到达服务器