[apache/dubbo]为什么两次同样的请求，协议却不一样

环境：
jdk：19
dubbo：3.2.0.beta-5
springboot: 3.0.4

这是我的dubbo过滤器
@Activate(group = CommonConstants.CONSUMER, value = "cookieValidationFilter")
public class CookieValidationFilter implements Filter {
    @Override
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        RpcContext context = RpcContext.getServerContext();
        return invoker.invoke(invocation);
    }
}

这是我的controller：
@DubboReference
UserService userService;

@PostMapping(value = "/sign_in", consumes = MediaType.APPLICATION_FORM_URLENCODED_VALUE)
public ServerResponseEntity<Object> loginController(ServerHttpRequest serverHttpRequest) {
    RpcContext context = RpcContext.getServerContext();
    System.out.println("rest接口");
    System.out.println(context.getProtocol());
    System.out.println(context.getRemoteAddressString());
    System.out.println("-----------------------------------------");
    String userInfo = serverHttpRequest.getHeaders().getFirst(USERINFO);
    return userService.loginService(userInfo);
}

这是我的service：
@Override
public ServerResponseEntity<Object> loginService(String userInfo) {
    try {
        responseEntity = new ServerResponseEntity<>(0, "login success!", Decryptor.decrypt(userInfo));
    } catch (Exception e) {
        logger.info(e.toString());
    }
    return responseEntity;
}

这是我的consumer配置文件：
server.port=8081

spring.application.name=consumer
spring.cloud.nacos.discovery.server-addr=192.168.220.128:8848

dubbo.application.name=consumer
dubbo.registry.address=nacos://192.168.220.128:8848
dubbo.protocol.port=-1
dubbo.consumer.protocol=tri
dubbo.consumer.filter=appended
dubbo.application.qos-port=22223

这是打印结果：
这是客户端连续两次调用/sign_in的打印结果
rest接口
null
null:0
-----------------------------------------
rest接口
tri
null:0
-----------------------------------------

问：为什么前后两次协议打印结果不一样，第一次null，第二次是tri