Processing Dialog after QR Scan in Xamarin

I'm using QR Code Scanner in Xamarin App, when it scans the qr code, there are some operation it does which takes about a minute, while it's performing operation, I want to show a loading dialog on the screen. But, it isn't showing on the screen, and elsewhere in the app, it's working perfectly.

Code

var expectedFormat = ZXing.BarcodeFormat.QR_CODE;
var opts = new ZXing.Mobile.MobileBarcodeScanningOptions { PossibleFormats = new List<ZXing.BarcodeFormat> { expectedFormat } };
var scanner = new ZXing.Mobile.MobileBarcodeScanner();
var result = await scanner.Scan(opts);
if (result == null)
{
    // code

    return null;
}
else
{
    using (UserDialogs.Instance.Loading("Processing"))
    {
        // code
    }
}

UPDATE CODE SAMPLE

public async Task Verification(object sender, EventArgs e)
{
    try
    {
        var expectedFormat = ZXing.BarcodeFormat.QR_CODE;
        var opts = new ZXing.Mobile.MobileBarcodeScanningOptions { PossibleFormats = new List<ZXing.BarcodeFormat> { expectedFormat } };
        var scanner = new ZXing.Mobile.MobileBarcodeScanner();
        var result = await scanner.Scan(opts);
        if (result == null)
        {
            // Code
            
            return null;
        }
        else
        {
            try
            {
                // QR Scan Result
                string qr_scan = result.Response;

                var result = JsonConvert.DeserializeObject<QRScan>(qr_scan);

                await CreateConnection();
            }
            catch (Exception error)
            { }
            finally
            {
                // navigate to next page
                await NavigationService.NavigateToAsync<NextViewModel>();
            }
        }
    }
    catch (Exception error)
    { }

    return null;
}

public async Task CreateConnection()
{
    UserDialogs.Instance.Loading("Processing");
     
    if ()
    {
        try
        {
            // Code
        }
        catch (Exception error)
        {
            // Code
        }
        finally
        {
            await CreateFolder(default, default);
        }
    }
}

public async Task CreateFolder(object sender, EventArgs e)
{
    UserDialogs.Instance.Loading("Processing");

    try
    {
        // Code
    }
    catch (Exception error)
    {
        // Code
    }

    return null;
}  

from Processing Dialog after QR Scan in Xamarin