I have been having a hard time trying to update Fedora22 and came across a known bug https://bugzilla.redhat.com/show_bug.cgi?id=1220074
What happens is when DNF fails on a transaction it aborts the update and remove alls the downloaded files, aka if you just downloaded 720updates at 1.1GB and one of them has a transaction failure then when you go to try the update again it will re-download the files.
The recommendation was to modify the dnf.conf file [dnf.conf file is located /etc/dnf/dnf.conf]
to add the line
This however would not work as all this does is simply tell dnf to down remove the downloaded files but it needs the transaction to be successful otherwise my understanding and from what I have seen it still removes the files.
The problem I was getting seemed to be related to the google-chrome package which there are a number of bugs listed for. In order to get the dnf update working I told DNF to ignore any packet *google
sudo dnf upgrade –exclude google*
Once I had told dnf to exclude the google packages the upgrade worked perfectly and I finally have an updated Fedora :D the — exclude packagename* is a handy command to know if you fall into the update loop due to a bad package/repo config.