Fedora 28 : Can you fix your Fedora !?

Fedora Packages have a different installation and development process thanks to testing and development teams.
Note: The common user may have networking problems and these will still lead to further errors.
A common error that should be more documented and constrained is:
Error: Failed to synchronize cache for repo 'updates'.

If you did not have intruders in the computer or provider changes to modify this process, then here are some elements that help you understand how it works.
The process of cleanup of temporary files kept for repositories and update / upgrade is still a testing and development process.
This includes any such data left behind from disabled or removed repositories as well as for different distribution release versions.

• dnf clean dbcache : this removes cache files generated from the repository metadata and forces DNF to regenerate the cache files the next time it is run.
• dnf clean expire-cache : this marks the repository metadata expired and will re-validate the cache for each repo the next time it is used.
• dnf clean metadata : just removes repository metadata files which is uses to determine the remote availability of packages and will make to download all the metadata the next time it is run.
• dnf clean packages :  removes any cached packages from the system.
• dnf clean all : does all of the above.

You can mix these commands so you can get the desired effect with the shell tool dnf , see this example:

dnf update --refresh

This will make a update but with this feature: --refresh will set metadata as expired before running the command.