Flutter Firebase for web not working in release build

When I run the app in debug mode, everything works fine, but when I use any type of release build, including flutter run -d chrome --release I get the error No Firebase App '[DEFAULT]' has been created - call Firebase App.initializeApp() (app/no-app). The error comes from main.dart.js.

Index.html:

<script src="https://www.gstatic.com/firebasejs/8.6.1/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.6.1/firebase-analytics.js"></script>
<!--<script src="https://www.gstatic.com/firebasejs/8.6.1/firebase-auth.js"></script>-->
<script src="https://www.gstatic.com/firebasejs/8.6.1/firebase-firestore.js"></script>
<script type="module">
  const firebaseConfig = {
    apiKey: "___",
    authDomain: "___",
    projectId: "___",
    storageBucket: "___",
    messagingSenderId: "___",
    appId: "___",
    measurementId: "____"
  };
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);
  firebase.analytics();
  firebase.firestore();
</script>

main.dart:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  runApp(ModularApp(
    module: AppModule(),
  ));
}

I've been trying to figure out what could be the problem for a very long time now. It works perfectly on both Android and web debug, but gives this one error on web release.