I noticed the same behavior; there's something odd about the way Hotmail's servers handle the POP3 QUIT command. nPOPuk sends QUIT, the server responds with something like
+OK Microsoft Exchange Server 2016 POP3 server signing off.
and then nPOPuk times out waiting for the connection to be closed. The other mail servers I use (Verizon, GMail) all close the connection, and nPOPuk gets the socket closed event; and Hotmail used to do this, also. I have a beta version that detects the timeout and prevents the error, if you're interested in trying it.