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[modern elk]

Create brushes around it. What do you mean it goes outside the map, like you want players to see the skybox?

They can't be entities such as func_brush or func_detail

Load the point file to see where the leak is

Follow it, it's either a gap in your geometry or an entity origin in the void

You can select everything in the map then go to where it ends in the void to see if it's an entity origin