There is an issue with CentOS Stream 8 and the currently published samba-4.15.2-2.el8.
I am working on a compose that removes that build from the repo.
In the interim, if you need to perform an update before i get the new compose released .. place this:
exclude=*4.15.2-2.el8*
in your CentOS-Stream-AppStream.repo and CentOS-Stream-BaseOS.repo.
I should have this fixed within in the next couple of hours.
Thanks, Johnny Hughes