u/AsparagusOutside4286

I'm pretty new to Nomad and I'm already stumped. I'm making a model for a simple BJD and everything was going well until I decided it was time to split the head. (Pic1+2) The mesh is completely hollow where it shouldn't be. I can interact with everything in the light brown section between the outer and inner layer. (Pic 3) Attempting to use the fill tool anywhere gets me a broken mesh. (Pic 4) Any new attempts at boolean on fresh primitives AND fresh files get me broken mesh results now. I'm really not sure what I'm supposed to do here to fix it or what I did in the first place. I can remake this easily but I'd like to avoid it in the future too