Firestore Data Bundles: Named Query always returns `nil`

To reduce firestore cost, I'm trying to introduce Firestore Data Bundles into my project.

I've tried some steps below.

1. Create Bundle txt file and upload it to GCS.

[Cloud Functions]

import { getAdmin } from "../../util/firebase";
import * as firebase from "firebase-admin";
import * as fs from "fs";

export const bundleHomeNewUsers = async () => {
  const BUCKET_NAME = "my-project-firestore-data-bundles";
  const admin = getAdmin();
  const db = admin.firestore();

  const bundle = db.bundle("home-users");

  // Get 10 latest users.
  const querySnapshot = await db
    .collection("users")
    .orderBy("createAt", "desc")
    .limit(10)
    .get();
  const buffer = bundle.add("home-users-bundles-query", querySnapshot).build();

  //Create tmp local file to upload
  const bundledFilePath = `/tmp/bundle.txt`;
  fs.writeFileSync(bundledFilePath, buffer);

  //Upload bundle file to Storage
  const destination = `firestore-data-bundles/home_users_bundles.txt`;
  await firebase
    .storage()
    .bucket(BUCKET_NAME)
    .upload(bundledFilePath, {
      destination,
      public: true,
      metadata: {
        cacheControl: `public, max-age=60, s-maxage=60`,
      },
    });
  console.log(
    `Uploaded to https://storage.googleapis.com/${BUCKET_NAME}/${destination}`
  );
};

2. Here is generated txt file in GCS.

[https://storage.googleapis.com/my-project-firestore-data-bundles/home_users_bundles.txt]

139{"metadata":{"id":"home-users","createTime":{"seconds":"1646058787","nanos":2930000},"version":1,"totalDocuments":10,"totalBytes":"15264"}}354{"namedQuery":{"name":"home-users-bundles-query","bundledQuery":{"parent":"projects/my-project/databases/(default)/documents","structuredQuery":{"from":[{"collectionId":"users"}],"orderBy":[{"field":{"fieldPath":"createAt"},"direction":"DESCENDING"}],"limit":{"value":10}},"limitType":"FIRST"},"readTime":{"seconds":"1646058787","nanos":2930000}}}228{"documentMetadata":{"name":"projects/my-project/databases/(default)/documents/users/bTb06yIbG3eZK45PCCAOx1uhlhD2","readTime":{"seconds":"1646058787","nanos":2930000},"exists":true,"queries":["home-users-bundles-query"]}} 
... 

// Total 10 items

3. I've tried to load the bundle file in iOS project.

[MyFirestoreService.swift]

let urlString = "https://storage.googleapis.com/my-project-firestore-data-bundles/home_users_bundles.txt"

let url = URL(string: urlString)!
let bundle = try! String(contentsOf: url, encoding: .utf8)

let db = Firestore.firestore()
db.loadBundle(Data(bundle.utf8)) { progress, error in 
  print(progress?.totalDocuments) // 10
  print(progress?.documentsLoaded) // 0
  
  switch progress {
    case .success:
      db.getQuery(named: "home-users-bundles-query") { query in 

        if let query = query {
          print("Ready to use named query.")

        } else {
          print("Failed to get named query.")

        }
      }

    case .error:
       print("error: \(error.debugDescription)")
/*
 error: Optional(Error Domain=FIRFirestoreErrorDomain Code=2 "Loading bundle failed with unknown error" UserInfo={NSLocalizedDescription=Loading bundle failed with unknown error})
*/

    default:
      return
  }
}

[Firebase SDK log]

8.12.1 - [Firebase/Firestore][I-FST000001] Failed to GetNextElement() from bundle with error 'values' is missing or is not an array

8.12.1 - [Firebase/Firestore][I-FST000001] Progress set to Error, but error_status() is ok()

[Dev environment]

XCode 13.2.1
FirebaseFirestore 8.12.1

Any ideas? I think this is kind of multi bytes or charset issue.