I think it's related to the stage manager.
The bug appeared when I was using the computer, or when exiting the sleep maybe too.
It happened very frequently : it restarted the computer. (I sent the bug report to apple for that problem when asked).
But, currently the problem 'seem' to be gone, once I modifyed the settings of the OS.
I set the "Stage manager" to OFF in the settings.
And the problem seem to be gone, so I think that maybe it's related to it.
I'll report here if the bug re-happen until now. (during my work hours, where the use peak of the computer is at it's highest point).
Don't hesitate how I can help you more, as the bug is still here using the stage manager that I really want to use, as it's very powerfull, (A bit hard to get used to it (specially when using multiples desktop), but very cool anyway).
thanks a lot.