When posts are deleted by IP in the case of CP/gore spam, posts from that anon will be deleted in previous breads as well. Some anons are then posting rapidly in those old breads to fill them up, however it is causing them to bump to the top of the catalog.
If you feel the need to bump old breads, I encourage you to type "sage" (Without quotes) in the email field when you make your posts in the older breads, as that will prevent your posts from bumping them, otherwise it can confuse some anons.
See https://8kun.top/faq.html#what-is-sage