Array returns error, when i play in portrait mode

Question

Ive made a Flappy bird Clone. It works fine when i play in normal screen mode. (1920×1080). However, when i play in potrait mode, my Array is getting a 'undefined' Error.

I tought theres a problem, since i use windowHeight and windowWidth. Iam doing it in the p5 framework.

this.hits = function (bird) {
         if (bird.y < this.top || bird.y > windowHeight - this.bottom) {
             if (bird.x > this.x && bird.x < this.x + this.w) {
                 return true;
             }
         }
         return false;
  }

Here are the used variables: (not actual code)

Bird:

bird.y = windowHeight/2;
bird.x = windowWidth*0.2;

Pipes:

 var pipeSpace = random(250,600);
    var centerY = random(0,windowHeight/3.5);
    pipes.top = centerY - pipeSpace/2;
    pipes.bottom = windowHeight - centerY - (centerY + pipeSpace/2);
    pipes.x  = windowWidth*1.5; (this is the x  position(starting position) of the pipes)
    this.w = 40; (this is the width of the pipes)

This function gets called every frame, to see if a collision is happening, but after i pass the first "pipe", the game breaks and says the error said above.

Edit: the Error: pipes[i] is undefined

this is the part where it occurs: Theres actually more code, but it has nothing to do with my problem.

var pipes = [];

function setup() {
  bird = new Bird();
  pipes.push(new Pipe());

}
function draw(){
    for (var i = pipes.length-1; i >= 0; i--){
      if(pipes[i].hits(bird)){
          gameOver = true;
        }
    }
}