I've struggled the same problem and I think the problem comes from gnome failing to pop up the confirmation dialog. That's why there is nothing in the error logs.
So what I did is changing the window manager from gnome to xfce. That solved the problem.
It would probably work with another manager or there may be a fix for gnome but here is how to install xfce:
yum -y install epel-release #adding epel repository
sed -i -e "s/enabled=1/enabled=0/g" /etc/yum.repos.d/epel.repo # using it only when needed
yum --enablerepo=epel -y groups install "Xfce" #installing xfce
echo "exec /usr/bin/xfce4-session" >> ~/.xinitrc
If you prefer to install oracle via vnc then skip the last two lines and change the /home/vnc-user/.vnc/xstartup ( vnc-user is oracle at my box ) like this:
If you don't know how to install vnc server on your CentOS 7 or Fedora box here is a guide: https://www.howtoforge.com/vnc-server-installation-on-centos-7