UMG: Drag-drop widgets get stuck at (0, 0)

Reported on the dev forum, drag-drop widget is broken in the 5.1 Preview.
https://forums.unrealengine.com/t/unreal-engine-5-1-preview/662523/221

Anyone else having problems with UUserWidget::SetPositionInViewport()?
With 5.0.3 my drag-drop widgets (based on the official tutorial Creating Drag and Drop UI | Unreal Engine Documentation 1 ) worked perfectly fine, now they are all stuck at position

Unknown macro: {0,0}

(top left) and SetPositionInViewport() does not change anything, despite getting the correct position input values.

It seems they added a new subsystem for handling widgets (UGameViewportSubsystem), perhaps it’s not working correctly yet?

1. Using the 5.1 preview, drag and drop a widget to the canvas.
   • Please see Creating Drag and Drop UI - Unreal Engine Documentation 1

Result: The widget is stuck at position (0, 0).