Youtube Analytics API returns 403 forbidden even if token is valid

I have an issue with access to Youtube Analytics API for random youtube channels.

After a successful authorization with following scopes:

• https://www.googleapis.com/auth/youtube.readonly
• https://www.googleapis.com/auth/yt-analytics.readonly

I'm saving the token and refresh token in the database. Everything works well for some time. After a while (eg. three months) when my app makes a request, Google returns 403:

{
  "error": {
    "errors": [
      {
        "domain": "global",
        "reason": "forbidden",
        "message": "Forbidden"
      }
    ],
    "code": 403,
    "message": "Forbidden"
  }
}

but only for Youtube Analytics API, other endpoints in Youtube Data API works fine with this token. That happen for random accounts (channels). Owners of this channels didn't revoke access to my app, didn't change account password etc.

This issue affects about 40% of all channels in my application (the time when Youtube Analytics API stops working is different, from 1 to 6 months after obtaining OAuth2 token). Then I have to send them periodically a new authorization url.

Where is the problem?

This is how I generate an auth url and make requests:

• Auth URL:

  flow = client.flow_from_clientsecrets(
      secret_file_path,
      scope=["https://www.googleapis.com/auth/youtube.readonly",
             "https://www.googleapis.com/auth/yt-analytics.readonly"],
      redirect_uri=redirect_url,
      prompt="consent"
  )
  flow.params["access_type"] = "offline"
  url = flow.step1_get_authorize_url(state=state)
  
  

• Stats request:

  auth = client.OAuth2Credentials.from_json(credentials_from_db)
  http_auth = auth.authorize(httplib2.Http())
  api = discovery.build("youtubeAnalytics", "v1", http=http_auth,
                     cache_discovery=False)
  api.reports().query(
      ids="channel==%s" % channel_id,
      metrics="estimatedMinutesWatched",
      dimensions="video",
      start_date=start_date,
      end_date=end_date,
      max_results=20,
      filters="video=={}".format(",".join(video_ids))
  ).execute(http=http)
  
  

I'm using google-api-python-client 1.6.5

from Youtube Analytics API returns 403 forbidden even if token is valid