Simple really because that port is monitored by avast and it is expecting NNTP protocol traffic which it isn't getting when you use that port for a non-standard NNTP use.
avast for many months and years hasn't changed the monitoring of port 119 and for years it has been expecting NNTP traffic and would have failed then just as it has now. So all I can think of is that you disabled NNTP port 119 scanning in the Internet Mail provider, but after the update is is somehow enabled again. I don't know, I just know that this will happen when using ports 110 pop3, 25smtp, 11p nntp or 143 imap for any use other than that associated with the expected protocol it will fail in avast.