To fix this issue simply upgrade react-scripts package (check latest version with npm info react-scripts version):

1. Replace in your package.json "react-scripts": "^3.x.x" with "react-scripts": "^3.4.1" (or the latest available version)
2. (optional for some) Delete your node_modules folder
3. Run npm install or yarn install

Some people reported that this issue was caused by running npm audit fix (avoid it!).

If you have ejected, this is the proper way to fix this issue:

find this file config/webpackDevServer.config.js and then inside this file find the following line:

app.use(noopServiceWorkerMiddleware());

You should change it to:

app.use(noopServiceWorkerMiddleware('/'));

For me(and probably most of you) the service worker is served at the root of the project. In case it's different for you, you can pass your base path instead.

I've also faced this problem and figure out it by upgrading the react-scripts package from "react-scripts": "3.x.x" to "react-scripts": "^3.4.1" (or the latest available version).

1. Delete node_modules\ folder
2. Delete package-lock.json file
3. Rewrite the package.json file from "react-scripts": "3.x.x" to "react-scripts": "^3.4.1"
4. Install node packages again npm i
5. Now, start the project npm start

And it works!!