Thanks for your answer, it's appreciated.
About your link, Sorry yes this is not a "bug" but a problem. I don't really know the difference between "bug" and "having an issue", for me this is the same.
It happened long time ago now (some months). I re-installed Nginx that make my issue disapper. But this week end it happened again and every minute.
The only thing i did is to watch movies on my NAS.
The command line gave :
Right know i have no more probleme. That's strange.