Just come across this myself.
Long-running fediverse instances will likely have old copies of established aussie.zone actors, but federation will be broke for newer instances and/or newer actors.
Verifiable by doing something like:
WORKS:
curl --header 'accept: application/activity+json' https://reddthat.com/u/lodion
DOESN'T WORK:
curl --header 'accept: application/activity+json' https://aussie.zone/u/lodion
I chose reddthat.com because it seems like it has similar protection, but allows for AP requests. (other instances use non-CF solutions, but I imagine they've had to make similar tweaks).
It's been a couple of days, so it might be worth some pings: