Coding of this souls-like mechanic never works when full screen [help needed]

As you can see in the video, when I kill an enemy I got some points, but this only happens when the editor window is not full-screen, and when it’s full-screen, it doesn’t work. I got some other errors only in full screen too, so weird. Help really appreciated.
https://streamable.com/uudsp

If you are using widgets, then make sure the widget component is anchored. Anchoring the widget component keeps its location no matter the resolution size.