downgrade sprockets

config/environments/development.rb

@@ -62,6 +62,7 @@ Rails.application.configure do
   # Suppress logger output for asset requests.
   config.assets.quiet = false
   config.assets.debug = true
+  config.assets.unknown_asset_fallback = false
 
   # Raises error for missing translations.
   # config.i18n.raise_on_missing_translations = true