What does "Network interrupted; server closed" mean?
If you have the "File Expert with Clouds" application installed then it may be the culprit. I was having the same issue and suspected it may be that application because it seemed to start happening after I had started and then stopped the FTP server.
I removed the application and the messages stopped.
I then re-installed the application and everything was fine until I started and stopped the FTP server at which time the messages started to appear again.
I removed the application (permanently this time) and the messages have stopped again.
I didn't bother to check to see if I could connect to the FTP server when it was supposedly stopped but I may re-install the app one more time just to see if that's the case. I'll post the result here if I do get around to testing it... Paul