Weird graphical error in custom map

[TimProzz]

Hello there,

I'm currently creating Illusions of the Dead 2 (sequel to Illusions of the Dead).
I'm working on a large exterior map. I just started working on the map.

After 1 hour of mapping I decided to give it a look in game and came accross this weird graphical glitch I've not seen before (I also have not created a map this large before).

Video: https://www.youtube.com/watch?v=5D9yhcAa0nY (sorry about the background music I was listening to)

hpl.log as attachment (for info about renderer)

There's no fog in the map (yet).
I purposely made the map really bright to make everything easier to see.
I think it has something to do with the size of the map, not sure.
I used custom entities/static objects (large outside terrain used in In Lucy's Eyes).

Does somebody know what the problem might be?

Thanks,

TimProzz