Of course, I'm taking action, and on kbin.social, those posts have been removed, which you can verify. However, for some reason, it doesn't always federate with Lemmy. It used to work before, but practically after every Lemmy update, there's something to fix in the code, or it could be related to API limits because some requests receive a "fail" status in the queues. The same applies to spam from Lemmy instances - I had to manually clean up hundreds of posts from other instances because they didn't always send AP requests, which I verified in the logs.
Do you seriously believe that it's a matter of individual accounts, and banning a user solves the problem?