Additive Box Brush disappearing?

I have no idea what is going on

This is happening to the Linear Stair brush as well, it doesn’t happen often but it’s there. and it’s collision is also not there

-what happens when you rebuild your geometry (the rebuild button)
-how have you moved this part of the bsp?
-make sure that you dont overlap one side of the bsp brush with the other one :slight_smile: