I don’t know if this is the same question worded differently, but I’m unclear about what is supposed to be synced when a community gets federated.
Let’s say I’m the first one on my instance to sub to a community on another instance. At first it is of course empty because it hasn’t been federated, but after a few moments the posts, old and new, start to show up. However, existing votes and comments appear to not get pulled in - only new ones created after the moment the community was initially federated.
Naturally, I don’t expect votes, posts or comments from blocked users or instances to sync. But the rest should be IMO - at least lazily (e.g. only when you visit a post do comments and votes on it get pulled in).