Made Custom Event and called it from Event BeginPlay() on player character after the widget is spawned, no change.
Doesn’t show up without breakpoint, does with it.
Made Custom Event on GameMode to call it manually from console and it worked properly.
Though I noticed here also one thing:
Here you can see that widgets spawns “properly” with default values set on Designer calculated for screen 1920x1080, where resize function was not called yet.
Here above is screen AFTER launching the function for resize, might not be really visible with screenshot but the widget did got resized properly and adjusted to viewport.
In conclusion:
While called on BeginPlay(); from Player Character which spawns the widget and Construct(); from the target widget it does not work properly and completely dissapears for some reason without breakpoint.
While called manually or with a breakpoint on Construct(); or BeginPlay(); it works properly, so the function technically works properly.