RectTransform gives me different value depending on its enabled state when I hit play

I have a script where I set its property value based on RectTransform.

The weird behavior I am seeing now is that depending on whether this object was enabled or disabled when I first hit play, the returned value is different.

     private void Start()
     {
         // Default values if not set by user is determined by the size of this object
         if (PosUp == 0f) PosUp = gameObject.GetComponent<RectTransform>().rect.height; // sizeDelta.y;
         if (PosDown == 0f) PosDown = 0f;
     }

This script does the correct thing when this object was disabled when I hit play. This script does not do the correct thing when this object was enabled when I hit play.

What is going on? Why is RectTransform().rect.height different depending on the enabled state?

Also, this object has Content Size Fitter + Vertical Layout Group component attached to it. Every since I attached these two, I started seeing the behavior.

Thanks for any help!!