As @Tim had hightlighted to check I had my XmlWriterSettings incorrectly set
XmlWriterSettings xwsSettings = new XmlWriterSettings();
xwsSettings.CheckCharacters = false;
xwsSettings.CloseOutput = true;
xwsSettings.ConformanceLevel = ConformanceLevel.Document;
xwsSettings.Encoding = Encoding.UTF8;
xwsSettings.Indent = false;
xwsSettings.NewLineHandling = NewLineHandling.None;
xwsSettings.OmitXmlDeclaration = true; <---- should have been false;