dependent destroy issue

scheme.rb

class Scheme < ApplicationRecord
  has_one :logo, as: :imageable, class_name: 'Image', dependent: :destroy

  has_many :steps, class_name: 'Scheme::Step', dependent: :destroy
  has_many :screens,
           through: :steps, source: :steppable, source_type: 'Screen'
  has_many :screen_groups,
           through: :steps, source: :steppable, source_type: 'Screen::Group'
  has_many :scheme_responses, class_name: 'Scheme::Response'

  accepts_nested_attributes_for :screens

  enum type: {
    'Survey' => 0,
    'Story' => 1
  }
end

screen.rb

class Screen < ApplicationRecord
  has_many :choices, dependent: :destroy

  accepts_nested_attributes_for :choices, allow_destroy: true

  enum type: {
    multiple_choice: 0,
    multiple_select: 1,
    text: 2,
    number: 3,
    date: 4,
    read_only: 5,
    participant_ID: 6
  }

  self.inheritance_column = :_type_disabled
end

step.rb

class Scheme::Step < ApplicationRecord
  belongs_to :scheme
  belongs_to :steppable, polymorphic: true
end