it could be that your instance doesn't have the post (e.g. no one else in the instance is following the account). Fediverse stuff is weird in that regard where it won't fetch them from the other server either, but they will show up going forward if you follow the account.
@twistedtxb @dirtmayor Completely agree. The fact that people from all over the web using different services can engage is amazing (hello from mastodon!)