webpack Safari nested folder source map issue

This is a bare minimum repository to reproduce the following issue:
Safari web inspector does not show the original source code for entries that are inside nested folders.

Steps to reproduce:

  1. Install dependencies with npm install
  2. Build the assets with npm run build
  3. Start the server with npm run start
  4. Open the url from Project is running at <url> in Safari
  5. Open the Web Inspector
  6. Go to the Debugger or Resources tab
  7. See that nested.js is not available under src/nested

Demonstration:

Demonstration

simple.js is available
nested.js is not, because
src/nested is shown empty