Specifies if the server is active and can accept incoming connections.
This read-only property returns
True if the FTPS server is running and listening for incoming connections.
False is returned.
However, if the connection is lost on the socket level, there is no way to find out that the connection has been closed, and Active property can still be True. The only way to check the actual connection state is to send something and get an error if the connection has been closed. This is by design of TCP/IP.
Your code should always be ready to handle unexpected disconnections and other network errors and reconnect if needed.