UMG Problems with Testplay in Standalone

Hi there…

Since can´t get an Answer in the Forums, i post this Problem now here…

The Situation is, that my UMG is not working in Standalone Testplay, but in Viewport or Window it is!
Means… in “Selected Viewport” or “New Editor Window (PIE)”, all Buttons react, PreConstruct is fired and PrintStrings are shown.
BUT, in Standalone, nothing works…

Here´s a Video of the Situation:

I hope for your Help here… since this, i think Bug, annoys me … i completely redone every work of the last Week, and it results in the same Problem…