From what I gather (I don't run an instance), the posts can take a while to fetch, the comments don't get fetched at all (only new ones will be synced) and votes are kind of a mess and their display partially instance-specific.
Lemmy
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It's weird because some old comments are being fetched. Usually with no votes, as far as I can tell, but I haven't looked too closely.
It seems like when a community is novel to an instance and someone subscribes, it can take a few hours to pull down a copy of all the posts. Maybe pull down is the wrong word, but sometimes I'll be browsing new/all and dozens of posts from a new community will start flying in.
I believe a user on your instance needs to be subscribed to the community if you want your server to pull posts and comments. I recommend you set up an account with no admin privileges and use a tool like Lemmy Community Seeder to get that account subscribed to all the top communities.
EDIT: just realized this post is 16 days old. Gotta fix that sorting algorithm!