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, @seahorse@midwest.social has to approve everyone who joins, and that might weed out bad actors.
So what can you do? Upvote content liberally, downvote sparingly.
Yeah, I was against it at first, because I don't like options being taken from me, but the more I think about it, the more it makes sense.
The whole idea is based on the false equivalency that upvotes and downvotes are equal, when in fact people feel negatives much more strongly, and they also tend to have an oversized impact, like mentioned by OP.