Hi
Osmi informs that the multipolgon needs correcting 
https://tools.geofabrik.de/osmi/?view=areas&lon=149.15488&lat=-21.14709&zoom=17
I haven’t looked closely at this but expect that polygons with outer role are touching and this makes the multipolygon invalid.
You should use the osm wiki to understand what makes multipolygons invalid.
You should use building:part method instead of a multipolygon, but the individual parts don’t render on the map yet, so you may prefer to map each section as simple polygons instead. 