http://ja.aliexpress.com/wholesale?catId=0&initiative_id=AS_20151205231131&SearchText=bag+mens

を起点に、商品ページのURLリストを取得し、その数を出力します。
たまに、期待した出力である6が出力されるのですが、
下記のようなエラーが出てしまう時があります。エラー8割、正常2割くらいの割合です。
何が原因かがわからず、途方に暮れています。
何かヒントをいただけませんか？

require 'open-uri'
require 'nokogiri'
require 'pstore'
require 'anemone'
require 'open_uri_redirections'
require 'openssl'
require 'selenium-webdriver'
require 'capybara'
require 'capybara/poltergeist'
#require 'phantomjs'


class Crawl
  def get_html_obj(url)
    Capybara.run_server = false
    Capybara.register_driver :poltergeist do |app|
      Capybara::Poltergeist::Driver.new(app, {js_errors: false})
    end
    session = Capybara::Session.new(:poltergeist)
    session.visit(url)
    return Nokogiri::HTML.parse(session.html)
  end

  def get_page_list(url)
    url_list = Array.new
    doc = get_html_obj(url)
    doc.css('div[class = "ui-pagination-navi util-left"]>a').each do |page|
      url_list << page.attribute("href").text 
    end
    url_list = url_list.sort_by do |k|
      /(.+)(page=)([\d]+)/ =~ k
      $3.to_i
    end
    return url_list.uniq
  end

  def get_page_list_all(url,n)
    url_list_all = Array.new
    crawl_url = Crawl.new
    last_url = url

    n.times do |n|
      url_list = crawl_url.get_page_list(last_url)
      last_url = url_list.last

      url_list_all.concat(url_list)
    end    
     url_list_all = url_list_all.sort_by do |k|
      /(.+)(page=)([\d]+)/ =~ k
      $3.to_i
    end
    return url_list_all.uniq
  end

  def get_product_list(url)
    url_list = Array.new
    doc = get_html_obj(url)
    doc.css('a[class = "history-item product "]').each do |page|
      url_list << page.attribute("href").text 
    end

    return url_list
  end

  def get_product_list_all(url,n)
    url_list = Array.new
    get_page_list_all(url,n).each do |url_tmp|
      doc = get_html_obj(url_tmp)
      doc.css('a[class = "history-item product "]').each do |page|
        url_list << page.attribute("href").text 
      end
    end
    return url_list
  end


  def get_product_obj(url)
    obj = Crawl.new
    return obj.get_html_obj(url)
  end


  def get_product_objs(url)
    obj = Crawl.new
    products = Array.new
    urls = obj.get_product_list(url)

    urls.each do |url|
      products << obj.get_html_obj(url)
    end
    return products
  end

  def get_product_objs_all(url,n)
    obj = Crawl.new
    products = Array.new
    urls = obj.get_page_list_all(url,n)

    urls.each do |url|
      products << obj.get_html_obj(url)
    end
    return products
  end
end

init_url = "http://ja.aliexpress.com/wholesale?catId=0&initiative_id=AS_20151205231131&SearchText=bag+mens"

crawl = Crawl.new
puts crawl.get_page_list(init_url).count

C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/web_socket_server.rb:98:in `rescue in send': Timed out waiting for response to {"id":"8482ca9f-6a3d-40d2-b6b7-eb33c8327b41","name":"visit","args":["http://ja.aliexpress.com/wholesale?catId=0&initiative_id=AS_20151205231131&SearchText=bag+mens"]}. It's possible that this happened because something took a very long time (for example a page load was slow). If so, setting the Poltergeist :timeout option to a higher value will help (see the docs for details). If increasing the timeout does not help, this is probably a bug in Poltergeist - please report it to the issue tracker. (Capybara::Poltergeist::TimeoutError)
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/web_socket_server.rb:94:in `send'
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/server.rb:33:in `send'
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/browser.rb:340:in `command'
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/browser.rb:34:in `visit'
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/poltergeist-1.8.1/lib/capybara/poltergeist/driver.rb:95:in `visit'
  from C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/capybara-2.5.0/lib/capybara/session.rb:232:in `visit'
  from C:/Users/Akinori/Documents/NetBeansProjects/RubyApplication1/lib/main2.rb:20:in `get_html_obj'
  from C:/Users/Akinori/Documents/NetBeansProjects/RubyApplication1/lib/main2.rb:26:in `get_page_list'
  from C:/Users/Akinori/Documents/NetBeansProjects/RubyApplication1/lib/main2.rb:109:in `<main>'