### 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 EXTRA_KEYS_KEY = "extra-keys";
    String GENERIC_SERIALIZATION_NATIVE_JAVA = "nativejava";
    String GENERIC_SERIALIZATION_DEFAULT = "true";
    String GENERIC_SERIALIZATION_BEAN = "bean";
    String GENERIC_RAW_RETURN = "raw.return";
    String GENERIC_SERIALIZATION_PROTOBUF = "protobuf-json";
    String GENERIC_WITH_CLZ_KEY = "generic.include.class";
    /**
     * The limit of callback service instances for one interface on every client
     */
    String CALLBACK_INSTANCES_LIMIT_KEY = "callbacks";
    /**
     * The default limit number for callback service instances
     *
     * @see #CALLBACK_INSTANCES_LIMIT_KEY
     */
    int DEFAULT_CALLBACK_INSTANCES = 1;
    String LOADBALANCE_KEY = "loadbalance";
    String DEFAULT_LOADBALANCE = "random";
    String RETRIES_KEY = "retries";
    String FORKS_KEY = "forks";
    int DEFAULT_RETRIES = 2;
    int DEFAULT_FAILBACK_TIMES = 3;
    String REGISTER_KEY = "register";
    String DUBBO_INVOCATION_PREFIX = "_DUBBO_IGNORE_ATTACH_";
    String INTERFACES = "interfaces";
    String SSL_ENABLED_KEY = "ssl-enabled";
}