Hi,

What does a 'cat /proc/PID/limits' (replace PID with the NGINX PID number) show you ?

The limits.conf file does not apply to systemd services.
Edit the file /lib/systemd/system/nginx.service and within the '[Service]' section the following: LimitNOFILE=65536
After that run: systemctl daemon-reload && systemctl restart nginx

Wesley