TLDR: 3 people working together can gatekeep content on the "active" and "hot" feeds on smaller servers/communities.
After some playing around, I noticed posts disappear after reaching a threshold. A quick search later and I'm in the Lemmy docs reading about how this all works.
In plain English, any three people working together (or one person with three accounts) can stop posts from appearing on the default feed. Once a post reaches -2 it will only appear to people who browse "new." Edit: Of course, it reappears after it climbs above -2, but it's a race against the clock.
As a smaller server, we're vulnerable to this. But we also have some extra mitigations - namely, @[email protected] has to approve everyone who joins, and that might weed out bad actors.
So what can you do? Upvote content liberally, downvote sparingly.