The server is possible in a hang state. May I know how do you run your domino server it is an application or a service? If you encounter the same again I would suggest to run Manual NSD
For more information on running a manual NSD on different OS environment kindly refer to the link below
Crash is something it reports some error on the console and then panic the server, an automatic notes diagnostic is collected.
Do you mean to say the server console is not seen when this situation happens and no Domino task seen in the task manager (Windows)/process list of notes user (Linux) ?
OR Server console is seen however, the server doesn't show any text moving or it doesn't respond to Notes client or any server command which you type ?
It would be better to raise a support case to understand what is going wrong.