Hi Marc,
I did a lot of Investigation, but finally managed to isolate the circumstances in which the error occurs.
It happens when a tcp and upd connection are created.
var connectionInfo = new ConnectionInfo(new IPEndPoint(IPAddress.Parse("192.168.2.100"), Port));
var tcpConnection = TCPConnection.GetConnection(connectionInfo, true);
var updConnection = UDPConnection.GetConnection(connectionInfo, UDPOptions.None, true);
Then also NetworkComms.AppendGlobalConnectionCloseHandler doesn’t work anymore. The ConnectionClosedHandler is never called. So NetworkComms seems not to realize that the connection is closed.