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?
When someone on your instance subscribes to a community on another instance for the first time, it grabs a small amount of back history, and the other instance starts federating all new content to your instance as it generates.
There is no way to pull in a complete backlog of all history automatically, because it would be a large resource burden
However, what you can do is find content that you want to interact with on the remote instance, copy the URL and then search for that URL on your server. That will pull that content and its context to your instance.
Neat! Though it does not pull all context, just the "upstream" context. Meaning that if I search a post's or comment's URL, it will not pull in comments below it. But if I search a low-level comment, it will pull in all parent comments from that comment chain as well as the post itself. And, like another commenter mentioned, it will not pull in the votes.
EDIT: On second thought, what I call "upstream context" is probably what Lemmy technically considers simply "context", isn't it?