Google Cloud Platform - Iot Core - 由于服务器关闭，连接已关闭，这是什么原因造成的，他们是否有任何文档？

如何解决Google Cloud Platform - Iot Core - 由于服务器关闭，连接已关闭，这是什么原因造成的，他们是否有任何文档？

我正在尝试诊断我的 MQTT 客户端与 Google Cloud Platform IoT Core 断开连接的原因。设备按预期每 15 分钟愉快地 PINGREQing，但偶尔会抛出以下错误并且设备断开连接一段时间。离线时间并不总是相同，持续时间也不相同。

{
  "insertId": "r79rpxfdzvpw2","jsonPayload": {
    "resourceName": "projects/<PROJECT-ID>/locations/asia-east1/registries/<REGISTRY>/devices/3172119418069326","eventType": "disCONNECT","status": {
      "code": 14,"description": "UNAVAILABLE","message": "SERVER: The connection is closed because the server is shutting down."
    },"disconnectType": "SERVER","protocol": "MQTT","serviceName": "cloudiot.googleapis.com"
  },"resource": {
    "type": "cloudiot_device","labels": {
      "project_id": "<PROJECT-ID>","device_num_id": "3172119418069326","device_registry_id": "w<REGISTRY>","location": "asia-east1"
    }
  },"timestamp": "2021-04-19T00:31:59.101631259Z","severity": "ERROR","labels": {
    "device_id": "<DEVICE-ID>"
  },"logName": "projects/<PROJECT-ID>/logs/cloudiot.googleapis.com%2Fdevice_activity","receiveTimestamp": "2021-04-19T00:32:00.113014773Z"
}

是否有任何关于此错误及其发生原因的文档？设备能否收到此事件的通知并立即重新连接？

我无法找到有关此错误的任何信息。

附加信息： MQTT 客户端是一个 ESP32，通过 Google Arduino JWT 库 (https://github.com/GoogleCloudPlatform/google-cloud-iot-arduino)

连接到 IoT Core