AsyncTask stops working after some time

Question

I've been using AsyncTask for some time already and it never stopped working after some time like in this case. After I open my app for the first time everything works fine and I can execute AsyncTask many times.

The problem is after I close my app and put device to stand still for a couple of minutes, AsyncTask becomes impossible to execute. Usually it takes for 1-2 seconds to load data, but in this case it takes for a couple of minutes.

This is my AsyncTask:

class MyAsyncTask extends AsyncTask<String, Void, ArrayList<MyObject>> {

private ProgressDialog dialog;
private FragmentActivity context;

public MyAsyncTask(FragmentActivity activity) {
    context = activity;
    dialog = new ProgressDialog(context);
}

protected void onPreExecute() {
    this.dialog.setMessage("...");
    this.dialog.show();
}

@Override
protected ArrayList<MyObject> doInBackground(String... params) {
    HttpURLConnection connection = null;
    ArrayList<MyObject> objects = null;

    try {
        URL url = new URL(params[0]);
        connection = (HttpURLConnection) url.openConnection();
        InputStream in = connection.getInputStream();
        BufferedReader reader = new BufferedReader(
                new InputStreamReader(in));
        if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
            return null;
        }
        String line;
        objects = new ArrayList<MyObject>();
        MyObject mo = new MyObject();

        while ((line = reader.readLine()) != null) {
            // Process data
        }

        reader.close();

    } catch (Exception e) {
        return null;
    } finally {
        if (connection != null)
            connection.disconnect();
    }

    return objects;

}

@Override
protected void onPostExecute(ArrayList<MyObject> data) {
    if (dialog.isShowing()) {
        dialog.dismiss();
    }

    if (data == null) {
        Toast.makeText(context, "fail", Toast.LENGTH_SHORT).show();
    }

    else {

    }

}
}

One more thing I've noticed is that when I press back or home buttons on my device and go back on home screen, in LogCat I see this warning:

W/IInputConnectionWrapper(22155): showStatusIcon on inactive InputConnection

I thought that this warning only appears if I don't close my connection but connection.disconnect(); is always called inside finally block. This could maybe be a part of the problem.

What do you think could be a problem?

UPDATE1

Now I noticed that after a couple of minutes I receive the following exception:

java.net.SocketException: recvfrom failed: ETIMEDOUT (Connection timed out)