Getting a lot of "loading screen/ping stuck" on SG server

Can you please test if you can reach the AU gateway with your WinMTR? If that shows your trace is running smoothly, you may need to try running your trace to SG both while attempting to play Path of Exile and not playing on the SG gateway, and just confirming that there isn't some unusual filtering occuring by your modem/router/isp.

Just to advise further on this case, Hexagon there are some latency spikes occuring from the hop on the first node of your trace to your second node (perhaps between your router and the box owned by your ISP on the street, or directly to the ISP themselves. This may help your ISP identify the cause of the issue.

Just another check, are you able to actually get in-game? If so, you may be able to get more comprehensive traces from the IP addresses of our instance servers. You can find this in your Path of Exile/Logs/client.txt file.

We wish you luck in this case. Hopefully it gets resolved soon,