why does my player only some times go under the platform ?

HI,
Can any one please help me? When i start my game the player only some times goes under the platform and others the platform will stop the player from moving across it.

void Start () {
playerCollider = GameObject.Find (“player”).GetComponent ();
Physics2D.IgnoreCollision (platformCollider, platformTrigger, true);
}

void OnTriggerEnter2D(Collider2D other)
{
	if (other.gameObject.name == "player") 
	{
		Physics2D.IgnoreCollision (platformCollider, playerCollider, true);
	
	}
}

void OnTriggerExit2D(Collider2D other)
{
	if (other.gameObject.name == "player") 
	{
		Physics2D.IgnoreCollision (platformCollider, playerCollider, false);

	}
}

found my answer on youtube: (link below if interested