Prerender.io first hit missed

I installed prerender.io with Nginx on my Ember.js project.I use the Facebook debugger to check if the prerender is installed correctly. The problem:

Each first hit of the prerender is a fail. Unfortunately, Facebook caches this version, so it is the one that is displayed on the site.

When I ask "Fetch new scrape informations", I get a hit and the content is displayed properly.

How can I make the first try a hit?

GUESSES

Maybe there is a problem with window.prerenderReady, that is used in my project (ember-prerender)?

Maybe the Nginx configuration does not wait for the result of the caching, or the caching is too long?

INFOS

I use Nginx with the standard configuration recommended by prerender.io