祖先查询在api explorer中生成503错误代码

在APPSOT api资源管理器中运行带有祖先查询的下端点函数会返回503代码错误,而在本地主机devserver上的api资源管理器上运行相同的代码时效果良好。

@ApiMethod(name = "getConferencesCreated",
           path = "getConferencesCreated",
           httpMethod = HttpMethod.POST
        )
        public List<Conference> getConferencesCreated(final User user) throws UnauthorizedException {
            if (user == null) {
                throw new UnauthorizedException("Authorization required");
            }
            String userId = user.getUserId();
            Key<Profile> userKey = Key.create(Profile.class, userId);
            return ofy().load().type(Conference.class)
                    .ancestor(userKey)
                    .order("name").list();
    }