Lightmass behaves randomly, fully closed environment still randomly lit

Hello, it’s me again x3

I was wondering if anyone has encountered an issue like this in their life with Unreal;

If you look at my images, you’ll see that the Lightmass generally bakes totaly fine Exept for some randomly chosen objects.
All of the objects in the scene are all instances of exactly 4 meshes that have a Shadow map UV, that bake properly in other places of the scene and the scene has Lightmass blocking cubes under the terrain to prevent light leaking.

Yet no matter what I do, every time on these exact same spots in the map despite what objects I place there, I get these artifacts as if Lightmass entirely ignored the rest of the scene for them.
Is it possible I lack enough ram for it to work properly? I’ll continue to debug this, but it takes 1 hour to bake and if anyone has any help it would be greatly appreciated.