HeaderLinks.jsx has a dependency on react-popper, that is not listed in package.json. It could be included as a part of Material-UI, but I'm not sure which version that would be.

Please add react-popper and popper.js to package.json. Also notice, that if you use the latest version of react-popper, then the API has changed, so you will have to replace the <Target> component with the <Reference> component.

If you don't explicitly depend on react-popper, but rather on the one (potentially) bundled with the latest Material-UI, then an npm install loads the new version of react-popper used by Material-UI, and breaks HeaderLinks.jsx because of the new react-popper API.