Thumbnail previews and subscriber counts differ when connecting to a community from a separate Lemmy instance

Another Lemmy newbie question here.

I have subscribed to a small handful of Communities that live outside of Lemmy.world, and that worked easily enough. But I notice that when accessing them here rather than on their own servers they aren't quite in sync. Posts are in a different order or delayed when viewing them from Lemmy.world through my subscriptions, thumbnail images don't load, and the subscriber count in the sidebar is often much lower here than when viewing the Community on its host instance.

Is this intended behavior, a known issue with Lemmy, or something on my end?