### 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" />`
```

* The type of the log access
     */
    private String logger;
    /**
     * Registry centers
     */
    private List<RegistryConfig> registries;
    private String registryIds;
    /**
     * Monitor center
     */
    private MonitorConfig monitor;
    /**
     * Is default or not
     */
    private Boolean isDefault;
    /**
     * Directory for saving thread dump
     */
    private String dumpDirectory;
    /**
     * Whether to enable qos or not
     */
    private Boolean qosEnable;
    /**
     * The qos host to listen
     */
    private String qosHost;
    /**
     * The qos port to listen