Metadata Store Key was changed so that it is not compatible with 2.7.1.

The code is in org.apache.dubbo.metadata.identifier.MetadataIdentifier
public static final String SEPARATOR = ":";
    public final static String DEFAULT_PATH_TAG = "metadata";
    public final static String META_DATA_STORE_TAG = ".metaData";
    private String serviceInterface;
    private String version;
    private String group;
    private String side;
    private String application;
    public MetadataIdentifier() {
    }
    public MetadataIdentifier(String serviceInterface, String version, String group, String side, String application) {
        this.serviceInterface = serviceInterface;
        this.version = version;
        this.group = group;
        this.side = side;
        this.application = application;
    }
    public MetadataIdentifier(URL url) {
        this.serviceInterface = url.getServiceInterface();
        this.version = url.getParameter(VERSION_KEY);
        this.group = url.getParameter(GROUP_KEY);