Storybook: Storybook v5.3.19 build hangs after upgrading to Angular v10.0.9

[georgef3rd]

Describe the bug
Storybook v5.3.19 build hangs on random files within the 19% to 21% range after upgrading Angular 9 project to Angular 10.

info @storybook/angular v5.3.19
info
info => Loading static files from: ...
info => Loading presets
info => Loading presets
info => Loading custom manager config.
info => Loading config/preview file in "./.storybook".
info => Found custom tsconfig.json
info => Using default Webpack setup.
info => Using angular project '...' for configuring Storybook.
info => Loading angular-cli config.
info => Get angular-cli webpack config.
Starting type checking service...
Using 1 worker with 2048MB memory limit
20% building 87/109 modules 22 active ...node_modulesairbnb-js-shimstargetes2016.js

Just hangs at that 20% completion status and doesn't move after an hour or more.
Tried running the build multiple times, and it hangs on random files and between %19 to 21% completion.

To Reproduce
Steps to reproduce the behavior:

1. Upgraded our Angular v9 library and Angular app to Angular v10.
2. Cleaned node_modules and dist folders.
3. Rebuilt Angular lib and app. Both Angular library and app work fine.
4. Run start-storybook.
5. Build hangs on random files in the 19% to 21% completion range as shown in the log output above.

Expected behavior
Storybook build should complete and serve Storybook web site.

Screenshots
N/A

Code snippets
N/A

System:

OS: Windows 10 10.0.17763
CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz

Binaries:
Node: 10.22.0 - C:Program Filesnodejsnode.EXE
npm: 6.14.6 - C:Program Filesnodejsnpm.CMD
Browsers:
Chrome: 84.0.4147.125
Edge: Spartan (44.17763.831.0)
npmPackages:
@storybook/addon-actions: ~5.3.19 => 5.3.19
@storybook/addon-knobs: ~5.3.19 => 5.3.19
@storybook/addon-links: ~5.3.19 => 5.3.19
@storybook/addon-notes: ~5.3.19 => 5.3.19
@storybook/addons: ~5.3.19 => 5.3.19
@storybook/angular: ~5.3.19 => 5.3.19

Additional context
Had to increase max memory for node usage for our app after upgrading to Angular 10. Tried increasing node's max memory before running start-storybook, but that did not help.

Requesting any help with troubleshooting this issue.

[georgef3rd]

Found out some additional information.

We're using this line:

import '!style-loader!css-loader!sass-loader!../src/styles.scss';

in our config.js to process our scss. This made the Storybook build stop working after the Angular v10 upgrade.
If I take out sass-loader, the Storybook build completes. However, it gets scss releated errors.
My guess that this stopped working is because the versions of the packages (style-loader, css-loader and sass-loader) were updated by the Angular v10 directly or indirectly.

If I use just main.js which doesn't need that line to process scss, the storybook builds again and works.

I would like to use main.js but we have an external dependency that won't let us use that quite yet.

So, do you have any suggestions on how to troubleshoot and/or work around this issue?

Thanks

[georgef3rd]

Just in case someone else encounters the Storybook build hanging after upgrading to Angular 10, the issue turned out to be with an import of style-loader/css-loader/sass-loader that was in config.js. Removing that import and using preset-scss instead resolved the issue. My best guess is that one or more npm package upgrades as a part of the Angular v10 upgrade caused that import to break.

Thank you for your help. Closing this issue.