update:
it does import to blender, then exporting it UE also works but it creates a collision frame around it so i cant enter the house in player mode. i think this happens in the import process when it calculates collision objects.
i also tried opening the .obj file with open3d and perhaps a clue: it opens fine but also doesnt show any walls so somethings going on with those walls in the obj file.
[Open3D INFO] Skipping non-triangle primitive geometry of type: 20