I’ve passed this post over to the folks who maintain the CIQ mirrors for Rocky Linux.
I cannot replicate this behavior myself, so, it could be that you are hitting some sort of WAF on their side.
Are you updating a single system, or multiple systems all sharing the same IP? That could explain the intermittent behavior.
As a workaround, you may edit the files in for your repositories in /etc/yum.repos.d/ to change from mirrorlist to baseurl and point to any mirror that you find works, including the default option: dl.rockylinux.org, which is backed by our CDN (Fastly)–and should not block requests.