I usually have trouble upgrading because I keep a local repository of packages and because they are shared via NFS dnf treats them as local files and doesn't download them. I've worked around that (F25->F26) by disabling it temporarily and distro-syncing after update.

I've also disabled my squid package cache proxy just in case but still the problem remains. I haven't seen anything on the list and most of the google search results are not for F26 to F27 upgrades so does anyone have a clue what's going on?

Thanks,

Richard