MEL-SYD-MCY has jumped up in price as well even though there’s no direct flight. According to a Google Flights search, it is cheaper to go via AKL and SYD than it is just via SYD.
Perhaps the routing rules have changed?
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Possibly but then it's also a bit odd that the change if only occurring on Domestic Business class flights.
The Mel-Syd-Ool Y flex fares have gone up too, to $300~ they were previously $255-275~ somewhere in that vicinity.