pfSense

Reviewing /var/log/nginx-error.log I found the following message:

"ssl_stapling" ignored, no OCSP responder URL in the certificate

This is because there is no ssl_trusted_certificate directive in the nginx configuration and it has the ssl_stapling_verify on.

http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_stapling_verify
http://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_trusted_certificate