On patform Ubuntu16.04 64 bit and RaspberryPi3
In one of my projects I noticed that; when I lose my internet connection and getting internet back a short time after that; the networkAccessibility keeps being nonAccessible.
After some debugging I noticed that in QNetworkAccessManager in createRequest a QDisabledNetworkReply was returned if networkAccessible == NotAccessible.
And that a new session is started after that. So that will only happen when networkAccessible != NotAccessible.
(loosely related: There could also be some bugs in that networkAccessibleChanged is not always fired when I disconnect my internet during a request but that is another issue I think of which I do not have more details)
I got my ability to create successfull requests back after switching those 2 parts of code. As it looks like to me that you need to have tried to open a session to determine if there is a connection possible.
Therefore i have here my patch (which also contains the change mentioned above) (I must say that I dont fully understands the whole networking stuff architecture because I have not studied that):