can you see if the app has an advanced mode. if not, can you on the ipad log in via safari at 192.168.1.1 and give use the ai mesh snapshot of the speed at the bottom right of the ai mesh page

I haven't tried disabling the 2.4ghz, I will do that next time I call.
Yes our ouse is daily large and it does have thickish wall too.

I didn't say disable it, but you were connecting on the 5ghz band.

You may find that a different 2.4ghz and 5ghz band may help.

Also i would suggest trying a cable between the main router and the xt9s

Could it just be a routing issue to/from Australia? I assume the mobile works as it would use a different transport method?

The mesh roaming is likely the culprit. When you're on a long FaceTime call the iPad keeps trying to roam between the XT9 nodes and the RP-AX58, and that brief handoff kills the call.

A couple of things worth trying: first, check if band steering is enabled in the Asus settings and try disabling it — sometimes it aggressively pushes devices between bands mid-call. Second, during a call try staying in one spot close to a single node and see if the dropouts stop. If they do, that confirms it's a roaming issue.

Also worth checking: is the RP-AX58 set up as an AiMesh node or just as a separate access point? If it's not properly integrated into AiMesh it can cause exactly this kind of instability.

Interesting. Also you can push clients to only one node.......

If roaming is the problem; can you set up a guest network on one access point only and use that for video calls? You might need to disable automatic connection to the main network on the device you are using.

on merlin you can........ (not sure about stock)

You can also limit devices to mesh units. We don't know if this is the issue that the OP is facing