Lights Dissappearing

I have a building in .skp format that i reimport ater making some design changes. I have already put interior decoration, lighting, etc., in the building. After reimporting, not only the painted vegetation dissappears as usual but also my placed lights. I suspect this has something to do with me changing something in the building.

BUT WHY.

lights aren't attached to the building like painted vegetation. Interior lighting costs a lot of time to get done properly. I just lost half a day of work. Can someon explain why this is happening?