Children of Retainer Box cannot be interacted with when visibility is set to "Self Hit Test Invisible"

When there is a Retainer box with the visibility set to "Self Hit Test Invisible" and has children, the children cannot be interacted with. Children such as a button cannot be clicked. This issue can also affect children of the child of the retainer box (such as buttons in a scroll box if the scroll box is a child of the retainer box).

CL Tested in:
4.14.3 - 3249277 (Not occurring) (Issue occurs)
4.15.3 - 3450819 (Issue occurs)
4.16.1 - 3466753 (Issue occurs)

Regression:
This issue does not occur in 4.14.3 binary build of the engine

1. Create a new project (No template or starter content needed)
2. Create a new widget blueprint > Name it "Widget_BP" > Open Widget_BP
3. Add a Retainer Box to the canvas panel
4. Under the Retainer Box details panel under visibility set to "Self Hit Test Invisible"
5. Add a button as a child of the Retainer Box
6. Compile, Save, and close Widget_BP
7. Open the level blueprint
8. In the event graph On event begin play > Create the widget Widget_BP > Add it to the viewport > using the player controller reference Show the mouse cursor
9. Save the level blueprint and name the level "TEST"
10. PIE and attempt to click the button
    Result: The button cannot be clicked
    Expected Result: The button can be clicked.