Embed group report problem

Here are some additional information of what happened in the background:

Chrome Console:

Call Response:

{"error":{"code":"UnknownError","pbi.error":{"code":"UnknownError","parameters":{},"details":[]}}}

 Behaviour:

1. Embedding of reports that are directly attachted to my workspace works without any problem
2. Embedding of group-reports that are shared additionaly through a dashboard-sharing works even too
3. Group-reports with the correct permission for my user (i´m able to view them in powerbi online) cannot be embedded, instead of the report i get the message "This content is not available" and the error described above.

Access-Token Generation:

$session = $this->get("session");
        $provider = new \TheNetworg\OAuth2\Client\Provider\Azure([
            'clientId'          => $this->clientId,
            'clientSecret'      => $this->clientSecret,
            'redirectUri'       => $this->redirectUri,
            ''
        ]);
        if (!isset($_GET['code'])) {
            // If we don't have an authorization code then get one
            $authUrl = $provider->getAuthorizationUrl();
            $session->set("oauth2state",$provider->getState());
            header('Location: '.$authUrl);
            exit;

        } else {
            $token = $provider->getAccessToken('authorization_code', [
                'code' => $_GET['code']
            ]);
        }

Token - Values Dump:

array:7 [▼
  "token_type" => "Bearer"
  "scope" => "Dashboard.Read.All Dataset.ReadWrite.All Group.Read Report.Read.All"
  "ext_expires_in" => "0"
  "expires_on" => "1473745814"
  "not_before" => "1473741914"
  "resource" => "https://analysis.windows.net/powerbi/api"
  "id_token" => "...."
]

Question:

Is it possible that i have to do something additional to get an accesstoken that provides access to group workspaces instead of having only access to reports / dashboards that are directly attached to my workspace ?