I've been having some trouble recently with my Hotmail accounts. It started with one and has spread to the others: after nPOPuk sends the QUIT command, it gets a +OK response, but then the connection doesn't get closed and nPOPuk times out and reports an error. Here's an excerpt from the log:
[Hotmail] +OK Microsoft Exchange Server 2016 POP3 server signing off.
I think I remember someone reporting something like this before, but I couldn't find it when I searched for "hotmail" in this forum.