Accessing Custom Map gives a black screen with UI

Hi!

My modding shenanigans continue. I managed to make a flat map once, and run around in it.

I went with something more complicated this time. But when I enter the game, I am met with a black screen, there is a UI, and

The issue is as such:

The map looks like this in the Editor:

I did Rebuild Pathing and Build Map, though it says “cannot be saved” when the windows pop up?

Could anyone tell me the cause of this issue?

Is it because of raised terrain? Did I misplace my spawn?

Thank you for your help!

This seems to occur when offsetting the region that contains spawns to 288

Putting it at 0 is ok.

Could a dev or an expert please explain the logic/functioning behind this? I’m worried that I get black screens the further players get from 0. How does this work and why does this happens? What happens behind the scenes?

Thank you.