Created attachment 1429590 [details]
Output of dnf update
After upgrading fedora from 27 to 28 (mostly successfully) dnf fails to refresh it's repos, because every mirror returns a 404 error (See attachment).
A few hours later refreshing the repos succeeded.
Keeping the bug open anyway, because it might be of interest, that updating and installing packages was not possible directly after the release of fedora 28.