configuration looks good overall. If on the first load your website has /#/ or not, than I suggest you add this line of code:

void main() {
   WidgetsFlutterBinding.ensureInitialized();
   usePathUrlStrategy(); // <-- This line
   ...
   runApp(...);
}

to your main() function before runApp.

You also need to add

  flutter_web_plugins:
    sdk: flutter

to your dependencies and import it in the main.dart via

import 'package:flutter_web_plugins/url_strategy.dart';.

More infos here: https://docs.flutter.dev/ui/navigation/url-strategies

I hope this can fix your issue? =)