The discussion “Negative likes bug” began with wisewords reporting a bug where spam-liking a topic can result in a negative like count. However, pfaffman clarified that this feature is not part of Discourse core and is likely a plugin used by the site. pfaffman suggested that the issue is not a bug, but rather a deliberate feature, and that it only affects the user who is spam-liking, so it may not be a priority to fix. The site admins would need to be convinced that it’s a problem worth fixing.
This bug points out a bug where if you spam-like a topic, it will become a negative number eventually.
It seems like this bug is known from the forum I’m currently in. People abuse this just to ‘downvote’ posts, however, if you reload, the bug would be fixed and it was only visible to the person who spammed the like button anyway.
That’s a big part of why they aren’t in Discourse core.
Whoever is running whatever site it is, is using some plugin that implements those. It’s pretty likely that it’s working as expected.
You’ll need to convince the site admins that it’s a problem that they want fixed. If it affects only the user who is downgrading the post, it doesn’t seem like much of a bug.