My custom horizons didn’t load after my upgrade to 4.0. Originally it was in
C:\Users\$WindowsUser$\AppData\Local\Programs\Enscape\Renderer\SystemData\Textures\Horizons
It’s in a different folder now (note added subfolder “RenderHost”)
C:\Users\$WindowsUser$\AppData\Local\Programs\Enscape\RenderHost\Renderer\SystemData\Textures\Horizons