How to get the player's position on the screen in PlayerCharacter::BeginPlay ?

Hi, I am trying to get the player’s position on the viewport / screen in my player character’s BeginPlay function. But I am getting different results when running in viewport / new viewport window.

First, here’s the code:

When I play in viewport:
PlayInViewport

But when I play in a new viewport window, it doesn’t work at all…
PlayInNewWindow

Is this the intended way to get the player’s position on the viewport / screen? And is this a bug?
Also why is the first example returning (-2316, 1698)?

Any help or insight greatly appreciated!