Light cut in half

[MatiCekuriel]

Hi !
I'm trying once again to create a CS in Soma, but I'm having an issue : the point lights and spot lights are cut in half :
It only do it in the level editor, it's working fine in game and the map viewer, but that's still a problem as you can guess :/

Spoiler below!

It's not coming from the plane, it's doing this with every texture, walls, etc.
Do you have any idea how to fix this ? :/
Thank you !