Android BLE does not receive any beacon after it start for a period of time

Android BLE device does not receive any beacon after it starts for a period of time, My app have initialized BLE at the beginning. even I restart my app, it still doesn't work,I have to restart Bluetooth. I don't know why it happened. This is my code below:

public void initBLE() {
    // Use this check to determine whether BLE is supported on the device.
    // Then you can
    // selectively disable BLE-related features.
    if (!mActivity.getPackageManager().hasSystemFeature(
            PackageManager.FEATURE_BLUETOOTH_LE)) {
        if (CommonUtils.isDebug) {
            Log.d(TAG,
                    mActivity.getResources().getString(
                            R.string.ble_not_supported));
        }
        return;
    }

    // Initializes a Bluetooth adapter. For API level 18 and above, get a
    // reference to
    // BluetoothAdapter through BluetoothManager.
    final BluetoothManager bluetoothManager = (BluetoothManager) mActivity
            .getSystemService(Context.BLUETOOTH_SERVICE);
    mBluetoothAdapter = bluetoothManager.getAdapter();

    // Checks if Bluetooth is supported on the device.
    if (mBluetoothAdapter == null) {
        if (CommonUtils.isDebug) {
            Log.e(TAG,
                    mActivity.getResources().getString(
                            R.string.error_bluetooth_not_supported));
        }
        return;
    }
    mBluetoothAdapter.enable();
}

/** * Device scan callback. */

 private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() {

    @Override
    public void onLeScan(final BluetoothDevice device, int rssi,
            byte[] scanRecord) {

        final DevIBeacon ibeacon = BLEDevice.getDevicefromScanData(device,
                rssi, scanRecord);
        if (ibeacon == null) {
            return;
        }

        synchronized (mBLEList) {
            mBLEList.add(ibeacon);
        }
    }
};


 private void scanLeDevice(final boolean enable) {
    if (enable) {
        isScanning = true;
        mBluetoothAdapter.startLeScan(mLeScanCallback);

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

LeScanCallback does not receive any beacon..