Taking first steps on CentOS 7 1804.
Logging into the Gnome/Gnome classic desktop from gdm works only for root. For other users, the screen flashes and the login screen returns. KDE/Plasma login is successful but ends up with a black screen with mouse pointer while all desktop processes appear to be running.
The CentOS 7 system is running in a CentOS6 KVM virtual machine, which may be the problem. I have no physical machine for testing right now.
These logins work for non-root users when the system is built from the CentOS 7 DVD. The non-working installation stems from a kickstart install which essentially includes a much larger number of packages, some 6k vs. 2.5k from DVD install). Maybe there are conflicts, but I have not been able to isolate anything.