Xamarin.Forms FCM OnRefereshToken Method not calle

I have Implemented a Xamarin Pushnotification using FCM and my code looks like

 // This service handles the device's registration with FCM.
[Service]
[IntentFilter(new[] { "com.google.firebase.INSTANCE_ID_EVENT" })]
public class ZCFirebaseIIDService : FirebaseInstanceIdService
{

    #region override methods
    public override void OnTokenRefresh()
    {
        var refreshedToken = FirebaseInstanceId.Instance.Token;
        App.DeviceToken = FirebaseInstanceId.Instance.Token;
    }
    #endregion
}

Also I have added all required permission in AndroidManifest and its like

<uses-sdk android:minSdkVersion="14" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
<uses-permission android:name="android.permission.BIND_NOTIFICATION_LISTENER_SERVICE" />
<uses-permission android:name="android.permission.INTERNET" />
<application android:label="App name" android:icon="@drawable/icon">
    <provider android:name="android.support.v4.content.FileProvider" android:authorities="com.appname.fileprovider" android:exported="false" android:grantUriPermissions="true">
        <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths">
        </meta-data>
    </provider>
    <receiver android:name="com.google.firebase.iid.FirebaseInstanceIdInternalReceiver" android:exported="false" />
    <receiver android:name="com.google.firebase.iid.FirebaseInstanceIdReceiver" android:exported="true" android:permission="com.google.android.c2dm.permission.SEND">
        <intent-filter>
            <action android:name="com.google.android.c2dm.intent.RECEIVE" />
            <action android:name="com.google.android.c2dm.intent.REGISTRATION" />
            <category android:name="${applicationId}" />
        </intent-filter>
    </receiver>
</application>

it's perfectly fine in Debug mode but when I run the app in release mode OnTokenRefresh method not even called .

can anyone please suggest me how can I resolve this issue.

There is a known bug in FCM that even I faced when I was implementing the same in my android application

Java.Lang.IllegalStateException: Default FirebaseApp is not initialized in this process Make sure to call FirebaseApp.initializeApp(Context) first.

Which is a bug that you will also find in the Microsoft xamarin website where it shows the implementation of FCM which you can find here

Also, there is a Bugzilla report on the same here.

Steps to solve the issue:

Xamarin only gives you this:

This is a known problem that you can work around by cleaning the solution and rebuilding the project (Build > Clean Solution, Build > Rebuild Solution). For more information, see this forum discussion.

But I recommend you do the following to be sure.

Check if you are receiving notifications when in debug mode.
If not remove bin and obj folders from your Android project.
Clean build your solution and try again
If it works archive the application and in release mode, test if you are receiving notifications.(If it works on one device it will work in all).
Steps for archive can be found here