As far as I’ve seen FAQs is should be so but my test comment doesn’t appear on the host server, just on lemmy.world. Is this a sync issue, or a weird feature?
Yes, it’s supposed to be visible on every instance that’s federated with your own. It can sometimes take some time to sync between servers though, and I’d expect it to stay like that for a while. There will likely be improvements to the process once everyone’s sorted out the recent surge of new users.
I believe it will show up on the ones that your home server isn’t defederated with
I have a similar situation right now, with an entire community.
A while ago, I made /c/breath_of_the_wild and I’ve been creating a post almost every day. Those posts do show up on kbin.social so THAT one synced already, but even tho the community itself also exists on lemmy.ml there isn’t a single visible post yet.
I’ve been told that it will eventually sync on its own, but no idea how long it will take. I guess the Fediverse is a bit overwhelmed right now, with all of the ex-redditors suddenly joining.
It should be seen by other instances if they are federated (they have link between each other). There could be an issue with syncing I guess or the instance you commented on got defederated.