React TypeError: __WEBPACK_IMPORTED_MODULE_0_react__.PropTypes is undefined

I had the same problem and late noticed that I had a typo in my import statement.

Instead of:

import React from "react"

I had:

import {React} from "react"

import PropTypes from 'prop-types';

React.PropTypes has moved into a different package since React v15.5. Please use the prop-types library instead.

What version of React are you using?

I got this error when upgrading to React 16, and changing my react lines in package.json to:

"react-dom": "^15.1.1",
"react": "^15.1.1",

and then running npm install and npm start fixed it for me.