Building PDF with Prawn

job.rb

class CollapseLabelsJob < ActiveJob::Base
  queue_as :default

  def perform(tracking_sheet)
    
    pdf_paths, destination = tracking_sheet.pdf_paths, File.join(Rails.root, "tmp/#{SecureRandom.hex}.pdf")
    
    paths = pdf_paths.map{ |i| open(i).path }.join(' ')
    
    options = "-q -dNOPAUSE -dBATCH -sDEVICE=pdfwrite"
    system "gs #{options} -sOutputFile=#{destination} #{paths}"
    
    Prawn::Document.generate(destination) do
      groups = pdf_paths.in_groups_of(4,false)
      groups.each_with_index do |group, i|
        group.each_with_index do |path, index|
          image_path = "tmp/#{SecureRandom.hex}.jpg"
          
          options = {
            :trim => '+repage',
            :density => 150,
            :sharpen => '0x1.0',
            :quality => '100',
            :rotate => 90
          }.map{ |k,v| "-#{k} #{v}" }.join(' ')
          system "convert #{open(path).path} #{options} #{image_path}"
          
          position = [
            [:left, :top], [:right, :top],
            # [:left, :center], [:right, :center],
            [:left, :bottom], [:right, :bottom]
          ][index]
          image image_path, :position => position[0], :vposition => position[1], :height => 200
          FileUtils.rm(image_path)
        end
        start_new_page if group != groups.last
      end
    end
    
    tracking_sheet.update_attribute(:labels, File.open(destination))
    
    FileUtils.rm(destination)
    
  end
  
end

There are 5 images in this example, but for some reason some of them are getting bumped into additional pages instead of all rendering on the same page and I cannot figure why?

https://www.dropbox.com/s/2ce1yscqbdb5ndl/Screenshot%202015-06-01%2019.50.54.png?dl=0

Is there some kind of MB limit per page or something?