Ignoring header X-Firebase-Locale because its value was null - Yet app launches after a manual restart

Question

I have a very weird error. When I try to log in/sign up to my app the user gets authenticated in firebase but the screens don't change. What's more, if I manually restart my app the authentication screen changes, and the app works the way it is supposed to. I attach the snippets of code, responsible for authentication and debug console data.

Debug console:

W/System ( 7512): Ignoring header X-Firebase-Locale because its value was null. 2 I/System.out( 7512): (HTTPLog)-Static: isSBSettingEnabled false D/InputConnectionAdaptor( 7512): The input method toggled cursor monitoring off I/SurfaceControl( 7512): nativeRelease nativeObject s[470179726496] I/SurfaceControl( 7512): nativeRelease nativeObject

Code:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final Future<FirebaseApp> _initialization = Firebase.initializeApp();
    return FutureBuilder<Object>(
        future: _initialization,
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const CircularProgressIndicator();
          }
          ...
              home: StreamBuilder(
                  stream: FirebaseAuth.instance.authStateChanges(),
                  builder: (context, AsyncSnapshot<User?> userSnapshot) {
                    if (userSnapshot.connectionState == ConnectionState.waiting) {
                      return const CircularProgressIndicator();
                    }
                    if (userSnapshot.hasData) {
                      print('user  exists');
                      return MainScreen();        
                    }
                    print('user does not exists');
                      return AuthScreen();
                  }),
              routes: {
                RecipeDetailScreen.routeName: (ctx) => RecipeDetailScreen(),
                AddRecipeScreen.routeName: (ctx) => AddRecipeScreen(),
                AuthScreen.routeName: (ctx) => AuthScreen(),
                DiaryScreen.routeName: (ctx) => DiaryScreen(),
                MainScreen.routeName: (ctx) => MainScreen(),
                NutritionScreen.routeName: (ctx) => NutritionScreen(),
              },
            ),
          );
        });
  }
}

void authUser(
    String email,
    String password,
    String conPassword,
    bool isLogin,
  ) async {
    setState(() {
      isLoading = true;
    });
    FocusScope.of(context).unfocus();
    try {
      if (isLogin == false) {
        await firebaseAuth.createUserWithEmailAndPassword(
          email: email,
          password: password,
        );
      } else {
        await firebaseAuth.signInWithEmailAndPassword(
          email: email,
          password: password,
        );
      }

      setState(() {
        isLoading = false;
      });
    } on PlatformException catch (err) {
      print(err);
      var message = 'An error occurred, pelase check your credentials!';

      if (err.message != null) {
        message = err.message!;
      }

      Scaffold.of(context).showSnackBar(
        SnackBar(
          content: Text(message),
          backgroundColor: Theme.of(context).errorColor,
        ),
      );
      setState(() {
        isLoading = false;
      });
    } catch (e) {
      print(e);
      setState(() {
        isLoading = false;
      });
      rethrow;
    }
  }