With out doweling too much on your code, the first thing which is wrong is that you are allocating you QNetworkAccessManager in the thread's constructor, which means its thread affinity is the main thread and NOT your thread, at the same time your QNetworkRequest which you pass to your 'networkMgr' is in your new thread.
So with out looking much at the functionality you have a salad of mixed thread affinities.
Be sure to read QThread docs and how thread affinity is determined.
Fix your code acourdingly, and see if the problem is solved.
Post again, with the corrected code if you still have a probelm.