VirtualBox on my MacBook Pro so that I could run a virtual instance of Fedora 27. After the install finished, though, I found that the guest screen was repeatedly flickering. Not sure what the problem was, I started googling and found a forum that pointed me to Wayland as the culprit.
I logged out of Gnome, logged back in but first selected the settings gear and told GDM I wanted "Gnome on Xorg". Once I was logged in the flicker was gone.
I'm not entirely sure what the problem is, but at least at this point it's working.