Hi
"@ kadira/storybook": "2.35.3"

is using the old webpack 1 config again - see here node_modules\@kadira\storybook\dist\server\config.js:

exports.default = function (configType, baseConfig, configDir) {
  var config = baseConfig;

  var babelConfig = (0, _babel_config2.default)(configDir);
  config.module.loaders[0].query = babelConfig;

As you can see it uses module.loaders rather than module.rules.

I can't tell exactly at which version of storybook that bug was introduced but it is now breaking all my builds.