Strange effect that I never asked for

Hello there,

For some reason, sometimes the screen goes black in my map when playing.

It will also happen when I use the Action


Code:

Visibility - Create an initially Enabled visibility modifier for (Triggering player) emitting Visibility across (Playable map area)

When I'm looking at the replay of the map, and disable the fog of war in it, this same effect also happens.

Also, for some strange reason, in a specific place in my map, when you go there with your screen, the effect is removed, and everything is normal again, but no trigger says anything about removing any effect or destroying it.

This effect happens even if I haven't used a map optimizer,

I use World Editor.

I really have no idea what causes it, and it's quite annoying.

Thank you for your time.