Why can't babel find its helper functions when compiling style changes with webpack in watch mode?

Question

Having some issues with babel and webpack. I'm not sure what introduced this issue, Its been intermittent, happened a few days ago then went away after hours of trying to debug. I'm not sure what fixed it then.

webpack.config --- relevant parts of package.json

The project is a multi-page jQuery and Flask app that is being moved to React. We are also using react-bootstrap.

The issue is:

• When I make a change in a sass or css file
• After webpack compiles
• Babel can't find some of its helper functions. Either the paths cannot be resolved, or the wrong paths are being inserted.
• This only happens when webpack is running in watch mode. Restarting webpack will make the errors go away.
• The errors come back once I start watch mode again and make a change to any of my sass or css.

Some of the errors I've been getting on page load after compiling style changes:

1.

In console:Uncaught TypeError: dP.f is not a function

File in chrome inspector, _hide.js

var dP = require('./_object-dp');
var createDesc = require('./_property-desc');
module.exports = require('./_descriptors') ? function (object, key, value) {
  return dP.f(object, key, createDesc(1, value));
} : function (object, key, value) {
  object[key] = value;
  return object;
};

// WEBPACK FOOTER
// ./node_modules/babel-polyfill/node_modules/core-js/modules/_hide.js
// module id = 136
// module chunks = 17

2.

Error in console: Uncaught TypeError: __WEBPACK_IMPORTED_MODULE_4_babel_runtime_helpers_inherits___default.a is not a function

File in chrome inspector, PanelGroup.js - from react-bootstrap relevant parts.

import _inherits from 'babel-runtime/helpers/inherits';

var PanelGroup = function (_React$Component) {
  _inherits(PanelGroup, _React$Component);

3.

Error in console: __WEBPACK_IMPORTED_MODULE_3_babel_runtime_helpers_possibleConstructorReturn___default.a is not a function

File in chrome inspector, Collapse.js - from react-bootstrap relevant parts.

import _possibleConstructorReturn from 'babel-runtime/helpers/possibleConstructorReturn';

UPDATE:

rm -rf node_modules does not help. Making any change to the JS entry file for the page will cause webpack to recompile and the error to go away.