BLE API >= 21 in deep sleep

Question

I have the following Service in Android

public class MyService extends Service{
....
 @Override
    public void onCreate() {
    ....
    StartHandler();
   ....}
public void StartHandler(){

        handlerScan = new Handler();
        handlerScan.postDelayed(new Runnable() {
            public void run() {
                if (!STOP) {

                    scanLeDevice(true);

                    handlerScan.postDelayed(this, 8000);
                }else{
                    mBluetoothManager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);
                    mBluetoothAdapter = mBluetoothManager.getAdapter();

                    handlerScan.postDelayed(this, 3000);
                }
            }
        }, 500);
    }

.....
public void scanLeDevice(final boolean enable) {
        if(mLeScanCallback == null){
            mBluetoothManager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);
            mBluetoothAdapter = mBluetoothManager.getAdapter();
            try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); }
        }
        if (enable) {
            mHandler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        mScanning = false;
                        mBluetoothAdapter.stopLeScan(mLeScanCallback);

                    }
                }, 3000);

            mScanning = true;

            mBluetoothAdapter.startLeScan(mLeScanCallback);
        } else {
            mScanning = false;
            mBluetoothAdapter.stopLeScan(mLeScanCallback);
        }
    }
....

1. Question: If i use API < 21 it works in background sometimes, but if i use new API > 21 (MLEScanner) when display is turned off it doesn't work. Why? Is this a bug?

2. Question: In my StartHandler I want acquire wakelock for 3 second and release. considers, StartHandler is repeated. Wakelock work only first time. How can solve this? There is a solution for acquire wakelock on startlescan and release this in stoplescan?

I don't want use AlarmManager why i need of a handler postdelayed. Thank you