For example, I’m on Lemmy.sdf.org and I joined the [email protected] community. But there are many missing articles and comments. If I browse directly on Lemmy.ml for the same article there ~90% of comments are missing.
https://lemmy.ml/post/1152794 has 26 comments https://lemmy.sdf.org/post/11232 has 0 comments
If you are the first to subscribe to one from another region, it takes a while for comments to sync. Once it does, you can read and comment to your heart’s content.