Google action MediaResponse not working on some de

we are currently playing around with newly launched https://developers.google.com/actions/reference/rest/Shared.Types/AppResponse#mediaresponse

According to documentation we will receive a final Response after media is finished playing. This works well in simulator but on mobile devices and speakers it works intermittently

We only get this call back 2 or 3 times and sometimes never get it on either devices. As it works few times we are sure it's just google engine but want to make sure we are not doing anything wrong ourselves.

I am using my own backend and have our engine (Action SDK). I am expecting this response when playback finishes, but I only get this intermittently:

{
  "user": {
    "userId": "user-id",
    "accessToken": "access-token",
    "locale": "en-US",
    "lastSeen": "2018-03-18T17:44:51Z"
  },
  "conversation": {
    "conversationId": "1521395430917",
    "type": "ACTIVE",
    "conversationToken": "42"
  },
  "inputs": [{
    "intent": "actions.intent.MEDIA_STATUS",
    "rawInputs": [{}],
    "arguments": [{
      "name": "MEDIA_STATUS",
      "extension": {
        "@type": "type.googleapis.com/google.actions.v2.MediaStatus",
        "status": "FINISHED"
      }
    }]
  }],
  "surface": {
    "capabilities": [
      {"name": "actions.capability.SCREEN_OUTPUT"},
      {"name": "actions.capability.AUDIO_OUTPUT"},
      {"name": "actions.capability.WEB_BROWSER"}, 
      {"name": "actions.capability.MEDIA_RESPONSE_AUDIO"}
    ]
  },
  "isInSandbox": true,
  "availableSurfaces": [
    {"capabilities": [
      {"name": "actions.capability.SCREEN_OUTPUT"}, {"name": "actions.capability.AUDIO_OUTPUT"}
    ]}
  ]
}

That does appear to be a bug on Google's end. You should fill out a support form and specify

Your project id
That this is a bug report
That this is with the Action SDK
That you are not receiving the MEDIA_STATUS event when you are expecting it to
Exactly what it sounds like from the user side (what does the user hear? The audio ends and then what?)