I have also had spontaneous restarts some months ago, which later stopped. I am 90% sure that the time where they stopped, was when I updated from 6.0 to beta 6.51 3½ months ago.
I have lately seen a lot of people experiencing restarts. All of them ran version 6.0.
So my advice is: Get the latest beta. Version 6.0 is only a stable version by name.
