Hi
Dornoch Towers appears on osmi page as an orange dot…  
https://tools.geofabrik.de/osmi/?view=areas&lon=152.99889&lat=-27.28420&zoom=8&baselayer=Geofabrik%20Standard&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways

I am not familiar with mapping complex buildings but expect you don’t need a multipolygon for this building and as mapped it is an invalid mp in osm rules for mp (outer ways of a mp cannot be shared).
I expect the solution is to map the perimeter as a building with all tags and then map the building parts as you have already done and delete the mp.