I'm at work at the moment (so results will be different from when I'm at home, but not by much) and my previous post was spot on. A simple tracert shows Akami is routing traffic through their Netherlands servers which is something that has happened previously ( see this thread https://forums.elderscrollsonline.com/en/discussion/439549/oceanic-lag-now-300-400-ms-even-with-a-vpn-was-250-300/p2).
Anyone with basic geography knowledge would be able to conclude that routing Australian traffic through Asia - > Europe -> then the US is going to add a decent amount of latency and network noise. Last time it happened this affected our NZ brother's and sisters too, so I would assume they're in the same boat.
When the network is good and stable it routes Sydney -> L.A or Sydney -> Auckland -> LA via the Southern Cross Cable Network. When it's bad (like the last few days/week) it routes out through either the ASC, AJC or the Oman Cable which sends the traffic through asia and or the middle east on to europe and then finally to the US.
While I haven't done the standard tests yet, I'm pretty sure the routing for Australia has changed again since the maintenance and this could be your issue.
This has been an issue that pops up for aussie players from time to time, some times it fixes itself, other times enough of us have to make some noise. It's all to do with the Akamai routing and from time to time all network traffic from Australia gets routed in a completely stupid direction.
For the last 18 months I've had pretty steady latency averaging 220 with minimal disconnects. Noticed as soon as the maintenance was over latency was around 350 - 380. This was a major red flag and as someone that has been quite vocal in the past of routing issues for Aussies, I didn't even bother doing a test. I just "knew" what the issue was and how to fix it, immediately fired up mudfish (VPN) and logged back in, ping was stable again at 210 - 220 and no disconnect issues.