ImageStamp has stopped working properly since upgrade

We've recently upgraded from Aspose.Pdf 7.7 to 8.8 and all is going well except that the ImageStamp functionality seems to have changed. We use ImageStamp to watermark the pdf document with a logo on the top left. The functionality was working prior to the upgrade.

Platform: ASP .NET 4.0
Version: Aspose.Pdf 8.8
Problem: ImageStamp is no longer present in generated PDF document after upgrade.

See the code below:

Aspose.Pdf.Document pdfDocument = new Aspose.Pdf.Document(OriginalFilename);
                ImageStamp imageStamp = new ImageStamp(imageFileName);
                imageStamp.Height = 37;
                imageStamp.Width = 256;
                imageStamp.TopMargin = 10;
                imageStamp.LeftMargin = 10;
                imageStamp.Background = true;
                imageStamp.Opacity = 0.3;
                imageStamp.HorizontalAlignment = HorizontalAlignment.Left;
                imageStamp.VerticalAlignment = VerticalAlignment.Top;

                foreach (Page pdfPage in pdfDocument.Pages)
                  {
                    pdfPage.AddStamp(imageStamp);
                  }

                pdfDocument.Save(attachment);

I've tried looking through the upgrade documentation but I found no information regarding changes to the ImageStamp class. Thank you for your time.