The latest symlink for Koji's yum repos is a convenience for users. The symlink is volatile and changes every time a repo regenerates. This could lead to errors when the link changes during an operation.
Systems like mbs should access repos by their repo id. The Koji api will report which repo id is the current one for a particular tag. The repo url using this id is stable and will not change for the life of the repo.
The koji hub call to use is getRepo. E.g.
getRepo
repo_info = session.getRepo(tag_id)
The call will return the current active repo for the tag (or None if there isn't an active one).
Commit e68f5c4c fixes this issue
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/mbs/issues/1581
Please continue any further discussion there.