Styles aren't correctly attached to elements when using Create React App + CSS modules

🐛 bug report

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project
  adheres to.
• I have searched the issue tracker for an issue that matches the one I want
  to file, without success.

Description of the problem

If a CSS module className is added to an element before that className exists in the relevant CSS module file, CodeSandbox does not pick it up.

How has this issue affected you? What are you trying to accomplish?

This makes using CSS modules very difficult. It is possible to get CodeSandbox to pick up the styles again by changing the className on the element, saving, and then changing it back to the one you want

To Reproduce

1. Fork the sandbox at https://codesandbox.io/s/happy-hypatia-0fgip
2. After it has been forked, uncomment the code in App.module.scss
3. Expect that "Hello CodeSandbox" turns green.

Link to sandbox: link (optional)

Your Environment

Fork the linked sandbox and reproduce the issue by uncommenting the code in App.module.scss after the fork. Trace how the CSS module className is attached to the element; done means the “Hello CodeSandbox” text turns green without changing the className to trigger an update.