CRA: Fast Refresh breaks embedded DevTools backend

`TypeError: undefined is not a function (near '...e.sub...') (anonymous function) src/backend/index.js:26 23 | // DevTools didn't get injected into this page (maybe b'c of the contentType). 24 | return () => {}; 25 | } > 26 | const subs = [ | ^ 27 | hook.sub( 28 | 'renderer-attached', 29 | ({ View compiled (anonymous function) src/backend.js:179 176 | hook.emit('shutdown'); 177 | }); 178 | > 179 | initBackend(hook, agent, window); | ^ 180 | 181 | // Setup React Native style editor if the environment supports it. 182 | if (resolveRNStyle != null || hook.resolveRNStyle != null) {` React version: ## Steps To Reproduce 1. create-react-app 2. yarn add react-devtools 3. in index.js add import 'react-devtools' on first line 4. start react-devtools 4. start create-react-app devserver 6. go to localhost:3000 7. crash Link to code example: add react-devtools on first line of vanilla 'create-react-app' ## The current behavior <img width="941" alt="devtools" src="https://user-images.githubusercontent.com/5372632/101188389-f24a2e80-3655-11eb-9a6b-239ac8742eb1.png"> ## The expected behavior Debug-Session