Repository: create-react-app
Issue: Hanging at 'Files successfully emitted, waiting for typecheck results...'  when using custom loaders
Labels: needs triage,issue: bug report

### Describe the bug

Similar issue described here:
https://github.com/facebook/create-react-app/issues/8707

However, that specific issue seemed to have multiple causes, one of which was resolved. This bug is still prevalent. This bug was described in this specific comment in that issue: https://github.com/facebook/create-react-app/issues/8707#issuecomment-606475886
That issue seemed to affect ionic framework. The solution for them was to revert from `3.4.1` to `3.4.0`. However, I am using react-scripts 4.0.1

Essentially, using any webpack loader (at least the three I used) will leave CRA hanging on "Files successfully emitted, waiting for typecheck results..."
I've tested [workerize-loader](https://github.com/developit/workerize-loader), [worker-loader](https://github.com/webpack-contrib/worker-loader), and [comlink-loader](https://github.com/GoogleChromeLabs/comlink-loader) (as you can tell I'm trying to incorporate web loaders into my project). Using any of these will cause the typechecking step to hang. However, running `yarn tsc` will run fine.

### Did you try recovering your dependencies?

Doesn't make a difference. Problem is prevalent in a fresh CRA project.

### Which terms did you search for in User Guide?

Error not found there. Only instance I can find online mentioning this issue is here (https://github.com/facebook/create-react-app/issues/8707). No other mention of the issue seems to exist elsewhere (stackoverflow, other GitHub issues, etc).

### Environment

```
Environment Info:

  current version of create-react-app: 4.0.1
  running from /Users/noah/.npm/_npx/53533/lib/node_modules/create-react-app

  System:
    OS: macOS 11.1
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Binaries:
    Node: 14.8.0 - ~/.nvm/versions/node/v14.8.0/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 6.14.9 - ~/.nvm/versions/node/v14.8.0/bin/npm
  Browsers:
    Chrome: 87.0.4280.88
    Edge: 87.0.664.66
    Firefox: 84.0
    Safari: 14.0.2
  npmPackages:
    react: 17.0.1 => 17.0.1 
    react-dom: ^16.9.0 => 16.9.0 
    react-scripts: 4.0.1 => 4.0.1 
  npmGlobalPackages:
    create-react-app: Not Found
```

### Steps to reproduce

<!--
  How would you describe your issue to someone who doesn’t know you or your project?
  Try to write a sequence of steps that anybody can repeat to see the issue.
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(Write your steps here:)

1. Install one of the worker loaders.
2. Implement workers
    - Details here: https://github.com/facebook/create-react-app/issues/8707#issuecomment-606475886

Check relevant commit in the reproducible demo for exact steps.

### Expected behavior

CRA works like normal

### Actual behavior

```bash
> npm run start

Starting development server...

(Hangs on this step rather than proceeding to "compiled with warnings" or "compiled successfully")
Files successfully emitted, waiting for typecheck results...
```

![Screen Shot 2020-12-30 at 2 35 40 PM](https://user-images.githubusercontent.com/6739076/103379743-4ce77680-4aac-11eb-8baa-2da2f5e77207.jpg)

### Reproducible demo

Fresh CRA project: https://github.com/NoahBres/webpack-loader-bug

Relevant commit for all the worker implementaions: https://github.com/NoahBres/webpack-loader-bug/commit/261d1f92cb6b460094f2349ea008f329cd35d691