### 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 REMOVE_VALUE_PREFIX = "-";
    String PROPERTIES_CHAR_SEPERATOR = "-";
    String UNDERLINE_SEPARATOR = "_";
    String SEPARATOR_REGEX = "_|-";
    String GROUP_CHAR_SEPERATOR = ":";
    String HIDE_KEY_PREFIX = ".";
    String DOT_REGEX = "\\.";
    String DEFAULT_KEY_PREFIX = "default.";
    String DEFAULT_KEY = "default";
    String PREFERRED_KEY = "preferred";
    /**
     * Default timeout value in milliseconds for server shutdown
     */
    int DEFAULT_SERVER_SHUTDOWN_TIMEOUT = 10000;
    String SIDE_KEY = "side";
    String PROVIDER_SIDE = "provider";
    String CONSUMER_SIDE = "consumer";
    String ANYHOST_KEY = "anyhost";
    String ANYHOST_VALUE = "0.0.0.0";
    String LOCALHOST_KEY = "localhost";
    String LOCALHOST_VALUE = "127.0.0.1";
    String METHODS_KEY = "methods";
    String METHOD_KEY = "method";
    String PID_KEY = "pid";
    String TIMESTAMP_KEY = "timestamp";
    String GROUP_KEY = "group";
    String PATH_KEY = "path";
    String INTERFACE_KEY = "interface";
    String FILE_KEY = "file";
    String DUMP_DIRECTORY = "dump.directory";