Inside of boolean cutter object appears after import

The image above is that of a skeletal mesh I have modified in Blender with a Boolean modifier (FBX). Its a skyscraper and the cut ive made is for an elevator shaft, the white inside out cube you see is that of the object i used to make the difference cut in blender, can anyone tell me why i can still see it in unreal?

Maybe you should just export the selected objects you want
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