I am trying Lemmy for the first time, and have subscribed to a community on another instance as a test (https://sopuli.xyz/c/homebrewing).
I can see the posts come though, but few if any of the comments are there. Obviously if I visit the community directly they show up, but then I can’t post/comment as my account is with this instance.
I saw this posted yesterday too. I think you just wait a bit for the federation to kick in and cache the comments over on your instance.