Adding new objects to list

Question

I have a game where player jump over bricks and then those bricks disappear. When my player died I want to create those blocks again. Here are my block class

private Rectangle full, top;
    private Sprite sprite;
    private static ArrayList<Integer> list = new ArrayList<Integer>(); // list of block coordinates
    private int x, y; // block coordinates
    public static int count, discount; // count - all blocks // discount - removed blocks

        public WeekBrick(int x, int y){
            this.x = x;
            this.y = y;

            list.add(x);
            list.add(y);

            count++;
            discount = count;
            full = new Rectangle(0, 0, 64, 64); 
            top = new Rectangle(0, 46, 64, 20);
            sprite = new Sprite(TextureManager.weekBrick);
            sprite.setSize(64, 64);
            setPosition(x, y);
         }
    }

And here in main when my character died I check (when I touch the block I decrease my discount like that WeekBrick.discount--;)

if(WeekBrick.count != WeekBrick.discount){
        addWeekBricks();
 }

And here I add new Brick

private void addWeekBricks(){
    for(int i = 0; i < (2 * WeekBrick.count); i++){
        list.add(new WeekBrick(WeekBrick.getItemFromList(i), WeekBrick.getItemFromList(++i), true));
    }
}

And when I add my object to list I got this error

Exception in thread "LWJGL Application" java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
    at java.util.ArrayList$Itr.next(Unknown Source)
    at com.mygdx.game.MyGame.mainGame(MyGame.java:484)
    at com.mygdx.game.MyGame.render(MyGame.java:189)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:214)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:120)

Why I get this error? What I'm doing wrong? EDIT: When I make this

if(Gdx.input.isKeyJustPressed(Input.Keys.M)){
            for(int i = 0; i < (2 * WeekBrick.count); i++){
                list.add(new WeekBrick(WeekBrick.getItemFromList(i), WeekBrick.getItemFromList(++i), true));
            }
        }

in my render method and when I press M all work! So how is it possible? When I 'in' the game and press M all bricks update and all works fine, but when I lose I get that exception...