JsCollectionOptimizerLazy tries to aggregate external files

Possibly the same as 📌 Asset optimization breaks functionality Active

Had a look at the logic. I think the problem might be that preprocess is set to TRUE by default, and it's not set to false for external files automatically.

You could try explicitly setting preprocess: false in the library definition - or this MR might work, but I haven't tested it, just a theory.

I tried the MR and those suggestions to no avail. I noticed the problem was no longer happening for me so I backtracked over any changes and found out that I added a dependency on a completely different library, to a completely different library (on core/once) which causes some change in how the JS gets grouped.

As a test, I just added a dependency on core/once to the broken external library (which has no dependencies) and that also worked.

some-external-library:
  js:
    //domain.com/ext.js: { type: external, minified: true }
    //domain.com/ext2.js: { type: external, minified: true }
  dependencies:
    # Why is this needed? We don't know.
    - core/once

Can't figure it out but at least I know removing that seemingly innocuous library dependency triggers the issue.

The working JS output looks like:

It's me, hi, I'm the problem, it's me...

We had this code altering JS, removing it also fixes the issue.

function xxx_js_alter(&$javascript, AttachedAssetsInterface $assets) {
  $request = \Drupal::request();
  if ($request->getPathInfo() === '/xxx') {
    unset($javascript['core/misc/drupal.init.js']);
    unset($javascript['core/misc/drupalSettingsLoader.js']);
    unset($javascript['core/misc/drupal.js']);
  }
}

Though I'm not sure why doing that wiped out the rest of the JS, and how adding a dependency on core/once fixes it.

OK going to close this as cannot reproduce.