Hi, multipolygon relations cannot share sides.
These are the ones affected
https://tools.geofabrik.de/osmi/?view=areas&lon=144.83004&lat=-37.86905&zoom=18
You can see examples of how multipolygons are constructed here
https://wiki.openstreetmap.org/wiki/Relation:multipolygon
I suggest just using simple polygons instead of the multipolygons