Monkey patch to_partial_path to fix namespaced models (https://github.com/rails/rails/issues/21004)

application.rb

module ActiveModel
  module Conversion
    def to_partial_path
      original_path = self.class._to_partial_path
      parts = original_path.split('/')
      return original_path if parts.length == 2
      pluralized_parts = parts[0..-3].map { |p| p.pluralize }
      "#{pluralized_parts.join('/')}/#{parts.last(2).join('/')}".freeze
    end
  end
end