OnDrop only triggering intermittently

Questions & Answers
1

SITUATION:
I have the following script on a UI GameObject A:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;

public class ScriptA: MonoBehaviour, IDropHandler
{
    public void OnDrop(PointerEventData eventData)
    {
       Debug.Log("Drop");
    }
}

On another UI GameObject B I have the following script:


using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class ScriptB : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{    
    private Image image;

    void Start()
    {
        image = GetComponent<Image>();
    }

    public void OnBeginDrag(PointerEventData eventData)
    {
        image.raycastTarget = false;
        Debug.Log("Drag Start");
    }

    public void OnDrag(PointerEventData eventData)
    {
        Debug.Log("Dragging");
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        Debug.Log("Drag End");
        image.raycastTarget = true;
    }
}

The hierarchy is (in parent → child order) UI Canvas → Container Image → GameObject A → GameObject B.

Both GameObjects have Image components that block raycasts by default. Container Image has a Grid Layout Group of several elements and GameObject A has a Grid Layout Group of one element.

There are no other GameObjects involved.

The expected behavior is that I depress the mouse button on GameObject B and “Drag Start” is printed to console once followed by a large quantity of “Dragging” while the object is being dragged, then when the object is brought over GameObject A and the mouse button is released “Drop” is printed once followed by “Drag End” once.

PROBLEM:
The actual behavior is different in that only 5-20% of the time is “Drop” printed.

Any ideas why, presumably, OnDrop isn’t being called every time? Everything else works 100%, it’s just this one last factor and I cannot troubleshoot. It seems entirely random whether or not it is called, though as I said the odds are on the low end.