At the time that I had joined this instance, I believe none of the posts from !30rock@dubvee.org were viewable on this instance. When I subscribed to the community, most posts then became available, but few-to-none of the comments/votes did. Everything since subscribing is entirely in sync. Check it out yourself; when sorting by Old, you see many posts from well before I had joined this instance, but they do not have comments and have just the OP’s initial one upvote: https://feddit.org/c/30rock@dubvee.org?dataType=Post&sort=Old
I have noticed similar behaviour with other communities, so I don’t think “actions” are just stuck in the “queue” or whatever. Is there anything I can do to get my instance fully in sync with a particular community? Or could this only be remedied by an administrator of one (or both) of the instances?
TLDR: Not a bug, feature; Or works as intended:)
That is by design, if every instance automatically synchronized (federated) every post and every comment from every other instance …the whole fediverse would explode?:) well it would at least require a loot more resources hosting any/every instance.
As for the “loading history”, if you take a true url[1] of a post or comment, insert it into the search bar of your instance, it will load it (and it will be visible in the corresponding community). One problem are votes, afair lemmy does not even offer a mechanism to let other instances see all historical votes, do not confuse this with votes that are already federated, the moment you subscribed is the moment the instance hosting that community started forwarding everything happening from now on in that community to lemmy.ml (your instance).
[1] - true url here means from where the resource originates/which instance is hosting that comment/post/community; You can find it as the little fediverse button on each non-local resource (comment/post/community).
E: I see others beat me to it haha