function behave unexpectedly inside a coroutine.

the function look like t$$anonymous$$s:

 private void Shrink(Animation anim)
     {
         AnimationClip clip = new AnimationClip();
         clip.legacy = true;
 
         char[] c = { 'x', 'y', 'z' };
         float rot = Random.value * 360 - 180;
         Vector3 toPosition = transform.position + (Random.value * radius * 5 / 6 + radius / 6) * new Vector3(Mathf.Cos(rot), Mathf.Sin(rot));
         float scaleMul = Random.value / 4 + 1.0f / 2.0f;
         float duration = (transform.position - toPosition).magnitude / speed;
         for (int i = 0; i < 3; i++)
         {
             Keyframe[] keys;
             keys = new Keyframe[2];
             keys[0] = new Keyframe(0.0f, transform.position[i]);
             keys[1] = new Keyframe(duration, toPosition[i]);
             curve = new AnimationCurve(keys);
             clip.SetCurve("", typeof(Transform), "localPosition." + c[i], curve);
         }
         for (int i = 0; i < 3; i++)
         {
             Keyframe[] keys;
             keys = new Keyframe[2];
             keys[0] = new Keyframe(0.0f, transform.localScale[i]);
             keys[1] = new Keyframe(duration, transform.localScale[i] * scaleMul);
             curve = new AnimationCurve(keys);
             clip.SetCurve("", typeof(Transform), "localScale." + c[i], curve);
         }
 
 
         // now animate the GameObject
         anim.AddClip(clip, clip.name);
         anim.Play(clip.name);
     }

all it does is that it sort of animate the shrinking of a border and moving it to some random location inside a radius. the function works fine if I call it on its own but I want the function to be called every x seconds so I wrote t$$anonymous$$s coroutine:

 IEnumerator ShrinkCR(float time)
     {
         for (int i = 0; i < 3; i++)
         {
             yield return new WaitForSeconds(time);
 
             Shrink(anim);
         }
     }

and simply called it inside update():

 private void Update()
     {
         StartCoroutine(ShrinkCR(10));
     }

but when I do that the border goes crazy and instead going to some random location inside some radius it just accelerate to the right indefinitly. What did I do wrong????