When turn off/on Wifi or plug in/out ethernet sometimes we can see warning:
'QObject::disconnect: Unexpected null parameter'.
There is also a post on qt forum - https://forum.qt.io/topic/71117/warning-qobject-disconnect-unexpected-null-parameter-in-qnetworkaccessmanager
I attached simple project on which I can reproduce the issue.
Put a breakpoint on 'return' in 'myMessageOutput' function to see callstack.