### Environment

* Dubbo version: 3.1.0
* Operating System version: xxx
* Java version: 1.8
* Istio version: 1.13.2

### Steps to reproduce this issue

1. 运行Istio+proxyless [demo程序 ](https://github.com/apache/dubbo-samples/tree/master/dubbo-samples-xds )，启动后consumer能正常访问provider。
2. 扩大provider副本数为2， consumer无法感知到新增的provider节点，新增的provider节点也没有收到consumer的请求。
3. 删除provider对应的k8s service（取消服务注册），consumer没有感知到服务变化，仍然可以继续调用provider。
4. 恢复provider service后，重启consumer实例，consumer才可以正常发现2个provider节点。

} catch (Throwable t) {
                logger.error("Error when requesting observe data. Type: " + getTypeUrl(), t);
            }
        }, pollingTimeout, pollingTimeout, TimeUnit.SECONDS);
        observeScheduledMap.put(request, scheduledFuture);
        return request;
    }
    @Override
    public void updateObserve(long request, Set<String> resourceNames) {
        
        requestParam.put(request, resourceNames);
    }
    protected DiscoveryRequest buildDiscoveryRequest(Set<String> resourceNames) {
        return DiscoveryRequest.newBuilder()
            .setNode(node)
            .setTypeUrl(getTypeUrl())
            .addAllResourceNames(resourceNames)
            .build();
    }
    protected DiscoveryRequest buildDiscoveryRequest(Set<String> resourceNames, DiscoveryResponse response) {
        
        return DiscoveryRequest.newBuilder()
            .setNode(node)
            .setTypeUrl(response.getTypeUrl())
            .setVersionInfo(response.getVersionInfo())
            .setResponseNonce(response.getNonce())
            .build();
    }
    protected abstract T decodeDiscoveryResponse(DiscoveryResponse response);
    private class ResponseObserver implements StreamObserver<DiscoveryResponse> {