AWS IoT策略不允许Cognito WebSocket客户端订阅主题

Question

我有以下政策：

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect"
      ],
      "Resource": [
        "*"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Publish",
        "iot:Receive"
      ],
      "Resource": [
        "arn:aws:iot:eu-west-2:672904080113:topic/x/a/b"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Subscribe"
      ],
      "Resource": [
        "arn:aws:iot:eu-west-2:672904080113:topicfilter/x/a/b"
      ]
    }
  ]
}

这已分配给证书以及认知用户ID和池。通过物理设备和蚊子客户端，我可以订阅并发布到主题x/a/b。

问题是，我无法从WebSocket客户端订阅同一主题。发布随处可见。

如果我将iot:Subscribe的资源设置为*，那么我也可以从WebSocket客户端订阅主题，并且它开始获取消息。为什么会这样？