Like I just mentioned in another thread:
The destructor of the QThread subclass is executed in the thread where the QThread object lives in (usually same thread where it was created in), not in the thread being executed in QThread::run().
I'm not willing to start examining almost 400 lines of code throughly just for fun, but for what I can see, you are creating the socket in run() and then writing to it in the destructor. These two blocks of code become executed in different threads. I'm also suspecting you having the problem described in this thread.