Nginx stops responding after few seconds - nginx

Question

Debian 7.8, nginx 1.8.0
Reboot my server, call a page, got the page, access logs are correct.
5.49.32.xxx - - [06/Aug/2015:14:22:30 +0200] "GET / HTTP/1.1" 304 0 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.130 Safari/537.36"
5.49.32.xxx - - [06/Aug/2015:14:22:31 +0200] "GET /favicon.ico HTTP/1.1" 200 26 "http://f1.mydomain.fr/" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.130 Safari/537.36"
And after about 1 min of server up, nginx stops responding.
Nothing in access_log, nothing in error_log.
service nginx restart doesn't solve the problem. If I want to get a response, the only way is to reboot my server.
I checked my syslog and kern.log, I saw nothing interesting.
No idea where the problem could be...
Here is my conf:
server {
listen 80;
server_name
f1.mydomain.fr
;
root /var/www/mydomain/current/web;
access_log /var/log/nginx/mydomain-access.log;
error_log /var/log/nginx/mydomain-error.log error;
location / {
# For Symfony2
try_files $uri /app.php$is_args$args;
}
location ~ ^/(app|app_dev|config|app_test|clear|ocp|apcu)\.php(/|$) {
include /etc/nginx/fastcgi_params;
include /etc/nginx/conf/fastcgi;
}
location ~ /\.ht {
deny all;
}
}