Ground stops working and ball stops jumping

Hello there! I started learning Unity a few hours ago, fallowing some tutorials on the internet. I have made a very simple platform game, where a ball jumps from platform to platform by pressing W and moving with A and D. Very basic.

Eventhough, it looks like i made something wrong, cause I have 2 problems that show up.

1: sometimes the W (jump) doesnt work. In other words, when I want to jump from platform A to platform B and press W to do so, the ball won't react to it and just keep rolling. The funny thing is though that this only happens sometimes. Sometimes it works, sometimes it doesn't. I don't know why.

2: This one is pretty annoying. For some reason there is a limit to my level space: when I put a platform (the same as all the others, since I just copy the object) overpassing a limit in the map, the ground function stops working and the ball just falls through the object. It has something to do with the map, since I have moved the object to the side and then I can stand on one half but when I pass that certain point I just fall. I really don't know what the problem is.

I don't know if I made myself clear, maybe I should copy the script.

Anyway! Thanks in advance,

Here is the ball scrips (the ground has no scrips since it's a normal cube):

 #pragma strict
 
   var rotationspeed = 100;
 
   var jumpheight = 8;
 
   private var isfalling = false; 
 
   function Update () 
 
   {
     //Handle ball rotation.
     var rotation : float = Input.GetAxis ("Horizontal") * rotationspeed; 
     rotation *= Time.deltaTime; 
     rigidbody.AddRelativeTorque (Vector3.back * rotation); 
     
     if (Input.GetKeyDown(KeyCode.W) && isfalling == false) 
     {
         rigidbody.velocity.y = jumpheight; 
     }
     isfalling = true;
    }
 
    function OnCollisionStay () 
    {
     isfalling = false; 
    }