I converted this KML file to GeoJSON and some reason it put the Chatham islands 12000km to the left of New Zealand instead of 800km to the right. https://datafinder.stats.govt.nz/layer/104253-regional-council-2020-clipped-generalised/ Is this a bug with the to geojson due to misplaced international dateline and plotting it at the other side of the worlds map or is my government data messed up?

I worked out, it's that longitude at 180° is the point where we define the international dateline and the Chathams are on the other side of it. But on paper the dateline was moved for local convenience. So, not a bug.