Upgrade F26 to F27 issue

[Luigi Votta]

Hello I just tried to upgrade from F26 to F27.
rpmfusion-free and rmpfusion-nonfree Enabled, as with previous dnf system-upgrade ... from
F25 to F26 without problems.

Today I've the following issue: 
sudo dnf system-upgrade reboot, reboots two times, but upgrade doesn't start. 

(from journal) 
Starting System Upgrade using DNF...
nov 16 15:56:42 localhost.localdomain systemd[1]: Listening on D-Bus System Message Bus
Socket.
nov 16 15:56:42 localhost.localdomain systemd[1]: Starting Update the operating system
whilst offline...
nov 16 15:56:42 localhost.localdomain pk-offline-update[713]: another framework set up the
trigger
nov 16 15:56:42 localhost.localdomain audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295
ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=packagekit-offline-update
comm="systemd" exe="/usr/lib/systemd/
nov 16 15:56:42 localhost.localdomain audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295
ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=packagekit-offline-update
comm="systemd" exe="/usr/lib/systemd/s
nov 16 15:56:42 localhost.localdomain systemd[1]: Started Update the operating system
whilst offline.
nov 16 15:56:42 localhost.localdomain audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295
ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=fwupd-offline-update
comm="systemd" exe="/usr/lib/systemd/system
nov 16 15:56:44 localhost.localdomain systemd[1]: Received SIGRTMIN+20 from PID 355
(plymouthd).
nov 16 15:56:44 localhost.localdomain dnf[712]: Errore: Sincronizzazione cache non
riuscita per il repo 'updates'
nov 16 15:56:44 localhost.localdomain systemd[1]: dnf-system-upgrade.service: Main process
exited, code=exited, status=1/FAILURE
nov 16 15:56:44 localhost.localdomain systemd[1]: Failed to start System Upgrade using
DNF.

Thank you for any hints
Luigi