Unfortunately ActivityPub doesn’t seem to support batching, so each post, reply, or vote has to be sent one at a time to every instance the community is federated with. Plus order is important for some items (e.g. if you edit a post multiple times, you need to make sure they are processed in the right order or you get out of sync).

Some smart people are looking at solutions, hopefully it’s solved before everything collapses 😆.

It’s unfortunately dependant on ping. When we receive an incoming federation activity, Lemmy gets info about the new thing but often then needs to send an outbound request to fetch the rest of the details. It’s not until that request is complete that Lemmy can accept the next update. Until then, lemmy.world is just sitting there retrying to send the next one as Lemmy.nz won’t accept it until it’s done with the current one (no queue).

The further we are from Lemmy.world (distance between servers), the higher the ping and therefore the longer each post takes to process. Because we are hosted in NZ and they are hosted on the other side of the world (Europe I think?), we are disproportionately affected.