World Position Of Child Object Shifted After Parenting

For my UIs there is t$$anonymous$$s chain of $$anonymous$$erarchy created as follow

• MainCanvas(screenspace-camera, with plane distance 0.31(near plane is 0.3))

  EmptyPanel

      UI_A(with rect transform)
     
           UI_B(with rect transform)
  
  

Emptypanel contains a script that creates UI_A at runtime and parent UI_A to itself

 GameObject UI_A= Instantiate(g);
 UI_A.transform.position = transform.position;
 UI_A.transform.SetParent(transform);
 UI_A.transform.localScale = transform.localScale;

UI_A also contain a script that create UI_B w$$anonymous$$ch will attach itself to UI_A

 //script in UI_A
 void Start () {
 
         //float width = GetComponent<RectTransform>().rect.width;
         //float height = GetComponent<RectTransform>().rect.height;
 
         Vector3 pos = transform.position;
         pos += new Vector3(offsetFromEdge.x, offsetFromEdge.y, 0f);
 
         _UI_B = new UI_B(transform, pos);
 
     }

and in UI_B constructor:

 public UI_B(Transform parent, Vector3 pos)
 {
 
     GameObject obj = new GameObject();
     obj.AddComponent<Canvas>();
 
     var comp = obj.GetComponent<RectTransform>();
     comp.pivot = Vector2.zero;
     comp.anchorMin = Vector2.zero;
     comp.anchorMax = Vector2.zero;
 
     obj.transform.position = pos;
 
     obj.SetParent(parent);
     obj.localScale = scale;
 
 }

So, when offsetFromEdge is (0,0), UI_B appear nice at where it should be, right on top of UI_A with localPosition being (0,0,0). However when i set the value of offsetFromEdge to (1,1), UI_B localposition become insanely huge (3611.xx, 3611.xx, 0);

These values are displayed on the RectTransform component's Pos X and Pos Y w$$anonymous$$ch i believe is the same a UI_B's transform.localPosition.

I have no idea what causes t$$anonymous$$s behavior.