Gameobject reference disappears at start

My game has objects falling and the player moves (a cauldron) to collect them and gain points. I am trying to make a Slider into a progress bar by setting its value equal to the score. I also have some text above it that specifically states the number of points.

Here is the relevant code for that:

 var progressSlider : UI.Slider;
 var pointsText : UI.Text;
 public var points : int = 0;
 public var finished : boolean = false;
 
 function Awake() {
     progressSlider = GetComponent(UI.Slider);
     pointsText = GetComponent(UI.Text);
 }
 function Update () {
     CountPoints();
 }

 function OnCollisionEnter2D (other : Collision2D) {    
     if (other.gameObject.CompareTag("B-Ingredient")) {
         other.gameObject.SetActive(false);
         points = points + 5;
     } else if (other.gameObject.CompareTag("S-Ingredient")) {
         other.gameObject.SetActive(false);
         points = points - 5;
     }
 }
 function CountPoints () {
     progressSlider.value = points; //this is the line that the NullReferenceException refers to
     if (points >= 50) {
         finished = true;
     }
     pointsText.text = "Points: " + points.ToString;
 }

Note: the collision enter stuff refers to a Rigidbody that's in the script, but I took it out to make it more focused on the problem. The collision stuff definitely isn't the problem.

I used Debug.Log and found that the references to progressSlider and pointsText are returning null, and I understand why (sorta). I assigned the slider and text their GameObjects in the inspector, but once I start the game, they disappear from the inspector:

I'm wondering if this is a bug. In this script (not shown in the code portion), I call for a Rigidbody and that Rigidbody doesn't disappear at the start or return null. In Play Mode, I tried re-assigning the references (as in dragging the Slider and Text objects in their respective reference boxes) and it works exactly how I want it to after.

Does this have to do with how I called GetComponent for the UI elements or the fact that they're children of the Canvas object? Any help (even if it's just general code fixes) would be appreciated!