https://developers.weixin.qq.com/doc/offiaccount/Message_Management/Passive_user_reply_message.html 接口地址

 /**
     * 微信服务器回调
     */
    @Override
    public String getOpenidAndTicket(HttpServletRequest request, HttpServletResponse response) throws Exception {
        String message = "success";
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        Map<String, String> map = MessageUtil.xmlToMap(request);
        log.info(":::::::::微信返回map::::::::" + map.toString());
        String openid = map.get("FromUserName");
        String kfz = map.get("ToUserName");
        String MsgType = map.get("MsgType");
        log.info(":::::::::MsgType::::::::" + MsgType);
        log.info(":::::::::XConstants.MESSAGE_EVENT::::::::" + WXConstants.MESSAGE_EVENT);

        if (MsgType.equals(WXConstants.MESSAGE_EVENT)) {
            //从集合中，获取是哪一种事件传入
            String eventType = map.get("Event");
            //对获取到的参数进行处理
            String eventKey = map.get("EventKey");
            //扫描带参数的二维码，如果用户未关注，则可关注公众号，事件类型为subscribe；用户已关注，则事件类型为SCAN
            String ticket = map.get("Ticket");
            if (eventType.equals(WXConstants.MESSAGE_SUBSCRIBE)) {
//                    wxPolling(ticket);


                // 创建document对象
                Document document = DocumentHelper.createDocument();
                // 创建根节点bookRoot
                Element xml = document.addElement("xml");
                // 向根节点中添加第一个节点
                Element toUserName = xml.addElement("ToUserName");
                // 向子节点中添加属性
                toUserName.addCDATA(openid);
                Element fromUserName = xml.addElement("FromUserName");
                fromUserName.addCDATA(appFromUserName);
                Element createTime = xml.addElement("CreateTime");
                createTime.addCDATA(String.valueOf(System.currentTimeMillis()));
                Element msgType = xml.addElement("MsgType");
                msgType.addCDATA("text");
                Element content = xml.addElement("Content");
                content.addCDATA("关注回复");
                message = document.getRootElement().asXML();
                log.info("关注自动回复，openid{}，回复信息为：{}", openid, message);
            } e
            
        }
        log.info("返回微信服务器消息内容为：{}", message);
        return message;
    }

代码如上，第一次关注返回信息时正常，第二次扫码后会提示“该公众号提供的服务出现故障，请稍后再试”，请问是什么原因呢？