### Environment

* Dubbo version: 2.7.5
* Operating System version: win10 or centos7
* Java version: 1.8.0
* Zookeeper version: 3.5.6

### Steps to reproduce this issue
My previous dubbo service version was 2.7.3. Today, I upgraded to 2.7.5. I found that the metadata can't be displayed all the time. The dubbo service registry in zookeeper, but zookeeper not /dubbo/metadata node path view.  If I switch back to 2.7.3 and 2.7.4.1, it can be displayed. Are there any bugs? I need help~~

xml-config:
`<dubbo:metadata-report address="zookeeper://192.168.11.100:2181?backup=192.168.11.105:2181" />`
```

String SHUTDOWN_WAIT_KEY = "dubbo.service.shutdown.wait";
    String DUBBO_PROTOCOL = "dubbo";
    String DUBBO_LABELS = "dubbo.labels";
    String DUBBO_ENV_KEYS = "dubbo.env.keys";
    String CONFIG_CONFIGFILE_KEY = "config-file";
    String CONFIG_ENABLE_KEY = "highest-priority";
    String CONFIG_NAMESPACE_KEY = "namespace";
    String CHECK_KEY = "check";
    String BACKLOG_KEY = "backlog";
    String HEARTBEAT_EVENT = null;
    String MOCK_HEARTBEAT_EVENT = "H";
    String READONLY_EVENT = "R";
    String REFERENCE_FILTER_KEY = "reference.filter";
    String INVOKER_LISTENER_KEY = "invoker.listener";
    String DUBBO_VERSION_KEY = "dubbo";
    String TAG_KEY = "dubbo.tag";
    /**
     * To decide whether to make connection when the client is created
     */
    String LAZY_CONNECT_KEY = "lazy";
    String STUB_EVENT_KEY = "dubbo.stub.event";
    String REFERENCE_INTERCEPTOR_KEY = "reference.interceptor";
    String SERVICE_FILTER_KEY = "service.filter";
    String EXPORTER_LISTENER_KEY = "exporter.listener";
    String METRICS_PORT = "metrics.port";
    String METRICS_PROTOCOL = "metrics.protocol";
    /**
     * After simplify the registry, should add some parameter individually for provider.
     *
     * @since 2.7.0