Hello @Fabio_Bacigalupo ,
Welcome to The Community Forums! 
I saw that you haven’t had any response to this topic yet, were you able to find a solution to this?
If not, as mentioned by you
Do you mean that after successfully updating the server, you were able to use it without any issues and later when you shut it down and restarted it, the server started giving the error?
- Have you tried increasing the ulimit and restarting the server?
- All the resources available in this hardware are just for MongoDB or are there any other installations sharing the resources?
- Can you try to start the server without any additional connections/read/writes from the application?
There is a similar issue resolved, can you take a look at this?
Regards,
Tarun