title: Receiving only the last background silent push notification from GCM
body: <p>I'm developing an Ionic 2 app wich receives push notifications. It must receive silent background notifications, meaning the notifications don't get visible in system notification area. Instead, when the app is open, the notifications are sent to the app en it process the data received. It works except it receives only the last notification sent while the app was closed.</p>
  
  <p>Maybe it's a GCM message config missing.</p>
  
  <h3>Expected Behaviour</h3>
  
  <blockquote>
    <p>Receive multiple background silent push notifications.</p>
  </blockquote>
  
  <h3>Actual Behaviour</h3>
  
  <blockquote>
    <p>Receiving only the last background push silent notification.</p>
  </blockquote>
  
  <h3>Reproduce Scenario (including but not limited to)</h3>
  
  Steps to Reproduce
  
  <blockquote>
    <p>Send two or more silent background messages while the app is closed.
    Open the app. Only the last notification is received by the on receive
    listener.</p>
  </blockquote>
  
  Platform and Version
  
  <blockquote>
    <p>Android 5.1.1/6.0</p>
  </blockquote>
  
  (Android) What device vendor
  
  <blockquote>
    <p>Google</p>
  </blockquote>
  
  Cordova CLI version and cordova platform version
  
  <blockquote>
    <p>cordova --version                                    6.2.0 cordova</p>
    
    <p>platform version android                     5.1.1</p>
  </blockquote>
  
  Plugin version
  
  <blockquote>
    <p>cordova plugin version | grep phonegap-plugin-push   1.7.4</p>
  </blockquote>
  
  Sample Push Data Payload
  
  <pre><code>{
                  "delay_while_idle": true,
                  "priority": "high",
  
                  "data": {
                      "content-available": "1",                   
                      "notId": Date.now(),
                      "silenttitle": 'some title',
                      "silentmessage": 'some message'
                  }
  }
  </code></pre>
  
  <p>How could I receive all silent notifications sent to my app?</p>