WorldToScreenPoint bad return at large values

At certain camera angles and distances from targets, Camera.WorldToScreenPoint returns seemingly inversed numbers as the real value approaches +- infinity. I would expect a return of Vector3.positive/negativeInfinity in these cases, should I report this as a bug?

Anyway, I'm trying to stretch UI elements between 2 world points, whether they are on screen or not, and that completely breaks when that happens. How can I get around this limitation? (If the 2 points are off screen on opposite sides, the UI element should stretch across the entire screen.)

 Camera cam = Camera.main;
 cam.transform.rotation = Quaternion.Euler(47.902f, 0, 0);
 cam.transform.position = new Vector3(-9.820416f, 7.028483f, -7.202926f);
     
 Debug.Log(cam.WorldToScreenPoint(new Vector3(-21.83334f, -1.69f, -16.83333f))); // Correct (-619771.9, -670568.4, 0.0)
 Debug.Log(cam.WorldToScreenPoint(new Vector3(-21.83334f, -1.68f, -16.83333f))); // Correct (-1463491.0, -1582139.0, 0.0)
 Debug.Log(cam.WorldToScreenPoint(new Vector3(-21.83334f, -1.67f, -16.83333f))); // Incorrect (4071627.0, 4398110.0, 0.0)
 Debug.Log(cam.WorldToScreenPoint(new Vector3(-21.83334f, -1.66f, -16.83333f))); // Incorrect (852279.1, 919864.0, 0.0)

 using UnityEngine;
 
 [RequireComponent(typeof(RectTransform))]
 public class UIAlignToWorld : MonoBehaviour
 {
     public Vector3 leftWorldPoint;
     public Vector3 rightWorldPoint;
     Camera cam;
     RectTransform thisRect;
 
     private void Awake()
     {
         cam = Camera.main;
         thisRect = GetComponent<RectTransform>();
     }
 
     void LateUpdate()
     {
         var leftPosition = cam.WorldToScreenPoint(leftWorldPoint);
         var rightPosition = cam.WorldToScreenPoint(rightWorldPoint);
         transform.position = (leftPosition + rightPosition) * 0.5f;
 
         float ang = Vector2.Angle(Vector2.right, rightPosition - leftPosition);
         if (rightPosition.y < leftPosition.y)
             ang = 360 - ang;
 
         transform.localRotation = Quaternion.Euler(0, 0, ang);
         thisRect.SetSizeWithCurrentAnchors(RectTransform.Axis.Horizontal, Vector3.Distance(leftPosition, rightPosition));
     }
 }