Tested again, AU at least 340ms, EU at least 300ms, US at least 700ms, KR at least 280ms, in server selection page, all are unstable.
Thanks a lot for testing! I'm sorry that the KR server didn't help that much.
It might be possible to add a mainland China server, but it requires special permissions, so we'll have to investigate this further before we know for sure.
Thanks for your patience.
You're welcome :D