I'm trying to work out the cause. My ISP isn't choking it, we're getting what is expected from their end, and our ONT tests fine. I have just tried a different modem with slight improvement, slightly more improvement when the handheld phones are disconnected (battery out) and the microwave is turned off at the wall. I've also changed channels to reduce overlap there, but nothing is getting it even close to the 6300 I was getting, though it did improve from about 900 to 2300. Doesn't seem to make any difference how many devices are connected either; have tried it when I'm the only person up and no-one else is using devices with no improvement.

I've not tried it with ethernet yet, waiting on a cable that's long enough to test, it's on the way.

I've done a twitch bandwidth test on my PC, most of the options for Australasia come in around what I'm getting, but I'd think it would use the closest servers which are in Australia and come in around 4000 or 9000; the ones doing about what I'm getting are in Japan or Taiwan. Being an Xbox I don't think there's any way to change server unfortunately.

Hoping someone has some idea of what might be going on.

I'm running an Xbox Series X and my son has the same issues on the Xbox One so it's not the Xbox at fault. Our normal router is a Netgear AX8, but the Spark arcadyan is the one we borrowed so it's not brand related. Our ISP is Spark and we're on fibre 100.