Faces indexed by iOS/Android app are not detected by Android/iOS App - AWS Rekognition

So I have been working on a product (Android First and then iOS) for a long time that index faces of people using AWS Rekognition and when they are again scanned later, it identifies them. It's working great when I index a face from an Android device and then try to search it with an Android device. But if I try to search it later on iOS app, it doesn't find it. Same is the result if I go other way round. Index with iOS, search with Android, not found. The collection ID is same while indexing and searching on both devices. I couldn't figure out how is it possible that a face indexed by one OS type, same region, same collection, couldn't be found while on other device.

If anyone here could try and help me with the issue, please do. I'll be really thankful.

Update 1: I have called "listCollections" function on both iOS and android apps. Both of them are showing different list of collections. This is the issue. But I can't figure our why it is happening. The identity pool and region is same on both of them.

Here is my Android Code to access Rekognition:

mCredentialsProvider = new CognitoCachingCredentialsProvider(
        mContext,
        "us-east-2:xbxfxexf-x5x5-xax7-x9xf-x5x0xexfx1xb", // Identity pool ID
        Regions.US_EAST_2 // Region
);

mUUID = UUID.randomUUID().toString().replace("-", "");

mAmazonS3Client = new AmazonS3Client(mCredentialsProvider);
mAmazonS3Client.setRegion(Region.getRegion(Regions.US_EAST_2));
mAmazonRekognitionClient = new AmazonRekognitionClient(mCredentialsProvider);

if(!mAmazonS3Client.doesBucketExist(mFacesBucket)) {
    mAmazonS3Client.createBucket(mFacesBucket);
}

Log.i(TAG, "Uploading image to S3 Bucket");
mAmazonS3Client.putObject(mFacesBucket, getS3ObjectName(), new File(data[0].toString()));
Log.i(TAG, "Image Uploaded");

Image image = new Image();
try {
    image.setBytes(ByteBuffer.wrap(Files.toByteArray(new File(data[0].toString()))));
} catch (IOException e) {
    e.printStackTrace();
}

Log.i(TAG, "Indexing image");
IndexFacesRequest indexFacesRequest =new IndexFacesRequest()
        .withCollectionId(mFacesCollection)
        .withImage(image)
        .withExternalImageId(mUUID)
        .withDetectionAttributes("ALL");

mAmazonRekognitionClient.indexFaces(indexFacesRequest);

Here is my iOS code to access Rekognition:

func uploadToCollection(img: UIImage)
    {
        let myIdentityPoolId="us-east-2:xbxfxexf-x5x5-xax7-x9xf-x5x0xexfx1xb"

        let credentialsProvider = AWSCognitoCredentialsProvider(regionType: .USEast2, identityPoolId: myIdentityPoolId)
        //store photo in s3()
        let configuration = AWSServiceConfiguration(region: .USEast2, credentialsProvider: credentialsProvider)

        AWSServiceManager.default().defaultServiceConfiguration = configuration
        rekognitionClient = AWSRekognition.default()

        guard let request = AWSRekognitionIndexFacesRequest() else
        {
            puts("Unable to initialize AWSRekognitionindexFaceRequest.")
            return
        }
        var go=false
        request.collectionId = "i_faces" + self.firebaseID.lowercased() //here iosCollection will be replaced by firebase Current UserID
        request.detectionAttributes = ["ALL", "DEFAULT"]
        request.externalImageId = self.UUID //this should be mUUID, passed as parameter to this function
        let sourceImage = img
        let image = AWSRekognitionImage()
        image!.bytes = sourceImage.jpegData(compressionQuality: 0.7)
        request.image = image
        self.rekognitionClient.indexFaces(request) { (response:AWSRekognitionIndexFacesResponse?, error:Error?) in
            if error == nil
            {
                print("Upload to Collection Complete")
            }
            go=true
            return
        }
        while(go==false){}
    }

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