Rails getting uninitialized constant error when trying to instantiate class from module in controller

Question

I created a module with some utility classes. A class from this module is instantiated from one of my controller several times :

class Admin::Statistic::StatisticsController < Admin::Statistic::ApplicationController

  def index
    @data_global_turnover               = Elasticsearch::Graphes::Graph::Drilldown.new(model: :order, request_params: {nature: :total_turnover, year: 2016}).classic
    @data_average_basket                = Elasticsearch::Graphes::Graph::Drilldown.new(model: :order, request_params: {nature: :avg_basket, year: 2016}).classic
  end

The first call is working, but on the second call I get :

uninitialized constant Elasticsearch::Graphes::Graph::Drilldown

How is it that the constant can be initialized on the first call and not on the second one ? How do I fix that ?