UMG Drag and Drop stops working in a Packaged or Standalone Game

Drag and drop operations just become broken on packaged builds or launching stand-alone, despite working inside the Editor (PIE). This is a regression from 4.19.2 (CL-4033788).

This issue was reported and tested in 4.20.1 (CL-4233996) and reproduced in Main 4.21 (CL-4299102).

1. Download and open the attached project
2. Package the game or Play in Standalone
3. Click and drag off the boxes in the upper left-hand corner. Repeat this

Results: The first time an component is being dragged works as expected, after the second time they can't be dragged anymore

Expected: To be able to drag widget components every time