After update from F27, when I login, gnome-shell (on Wayland and Xorg) crashes and goto on login screen
This is happened on two my Notebook

In my case, I have resolve this problem goto on console (CTRL+ALT+F3), login with my account and remove all gnome shell extensions present into ~/.local/share/gnome-shell/extensions that were also installed via dnf

Thanks

-- 
Dario Lesca
(inviato dal mio Linux Fedora 27 Workstation)