Build fails: Could not find plugin "proposal-numeric-separator"

Created by: muehlbaueralex

Describe the bug

Running npm run build will fail on any project, even on a vanilla app created with create-react-app will fail with the following error:

Error: [BABEL] /Users/<username>/Projects/my-app/src/index.js: Could not find plugin "proposal-numeric-separator". Ensure there is an entry in ./available-plugins.js for it. (While processing: "/Users/<username>/Projects/my-app/node_modules/babel-preset-react-app/index.js$0")
    at Array.map (<anonymous>)
    at Generator.next (<anonymous>)
    at Generator.next (<anonymous>)


npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! my-app@0.1.0 build: `react-scripts build`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the my-app@0.1.0 build script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

From our build pipelines I can tell it started roughly around Mar 20, 2020 4:48pm GMT+0100

Did you try recovering your dependencies?

I tried recovering the module tree and even verified with a vanilla app. It happens on my local machine and on our build machines with no changes involved there.

$ npm --version
6.13.1

Which terms did you search for in User Guide?

(Write your answer here if relevant.)

Environment

$ npx create-react-app --info

Environment Info:

  System:
    OS: macOS 10.15.3
    CPU: (8) x64 Intel(R) Core(TM) i7-8559U CPU @ 2.70GHz
  Binaries:
    Node: 13.2.0 - /usr/local/bin/node
    Yarn: 1.19.2 - /usr/local/bin/yarn
    npm: 6.13.1 - /usr/local/bin/npm
  Browsers:
    Chrome: 80.0.3987.149
    Firefox: 68.0.2
    Safari: 13.0.5
  npmPackages:
    react: ^16.13.1 => 16.13.1
    react-dom: ^16.13.1 => 16.13.1
    react-scripts: 3.4.0 => 3.4.0
  npmGlobalPackages:
    create-react-app: Not Found

Steps to reproduce

npx create-react-app my-app
cd my-app
npm run build

Expected behavior

The build is successful with no error.

Reproducible demo

As mentioned in the above sections a vanilla app is enough to reproduce.

npx create-react-app my-app
cd my-app
npm run build