(I'm really not sure where to file this ...)
In  (brought in by openstack-release-train) it has the mirrorlist line
name=CentOS-$releasever - Ceph Nautilus
which I believe should have '$stream' instead of '$releasever'. I noticed because our jobs started failing when 8 was deprecated.
thanks for reporting this bug.
Actually this has been tracked already via , and it's going to be solved by  in the TripleO context.
As per , centos8 is EOL, and most of the repos has been removed at the end of January, therefore
nautilus was rebuilt in 8-stream .
If you think there are still issues with train/nautilus, you can open a ticket here https://pagure.io/centos-infra/issue.