Repository: create-react-app
Issue: Duplicate Websocket connection only in dev mode
Labels: needs triage,issue: bug report


### Describe the bug

WebSockets created conditionally and set on a `useRef` connect twice. This only happens when the app is started in development mode with `yarn start` but not when the app is served in production from the files generated by `yarn build`.

### Did you try recovering your dependencies?

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Yes

### Which terms did you search for in User Guide?

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useRef, websocket

### Environment

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```
Environment Info:

  current version of create-react-app: 4.0.1
  running from /home/chetan/.npm/_npx/1695019/lib/node_modules/create-react-app

  System:
    OS: Linux 5.8 Ubuntu 20.04.1 LTS (Focal Fossa)
    CPU: (12) x64 Intel(R) Core(TM) i7-10710U CPU @ 1.10GHz
  Binaries:
    Node: 12.20.1 - ~/.nvm/versions/node/v12.20.1/bin/node
    Yarn: 1.22.10 - ~/.npm-packages/bin/yarn
    npm: 6.14.11 - ~/.nvm/versions/node/v12.20.1/bin/npm
  Browsers:
    Chrome: Not Found
    Firefox: 84.0.2
  npmPackages:
    react: Not Found
    react-dom: Not Found
    react-scripts: Not Found
  npmGlobalPackages:
    create-react-app: Not Found
```

Tested on Chromium 87.0.4280.141 and Firefox 84.0.2 on Ubuntu 20.04.

### Steps to reproduce

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```shell
yarn
yarn start
```

### Expected behavior

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One websocket connection is made to `echo.websocket.org`.

### Actual behavior

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Two websocket connections are made to `echo.websocket.org`, which are visible in the "Network" tab in browser dev tools.

![Screenshot from 2021-01-14 16-27-45](https://user-images.githubusercontent.com/292958/104619200-819b2680-5685-11eb-8ab0-cb20f0f2d0bd.png)


### Reproducible demo

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https://github.com/chetbox/react-dev-websocket-bug

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