I just noticed one post had a negative amount of comments showing on it.
Link to post (NSFW): https://lemmynsfw.com/post/230692
This is a known lemmy bug (not unique to your app), when you delete a comment it puts the comment counter down by 1 every time you hit the delete button, instead of just 1 overall.
This means I can delete the same comment and, before it refreshes, delete it several more times and trick the instance into thinking I've deleted more comments than exist.