I am seeing odd behavior on my X11 server on CentOS 6. X11 Forwarding works as you would expect. I can ssh (with -Y or -X) from CentOS 6 and launch & display xclock, but I can’t do the same for other applications like gnome-terminal or gedit—they just don’t display and their process is killed. The strangest part, is that if I connect into that same original CentOS 6 host from Windows first (via Putty) and use Exceed or Xming on Windows, I can then launch all applications without issue. So it seems to be an issue with the native X11 server on CentOS 6. If I turn verbose mode on for ssh, I do not get any errors, and X11 specific apps work just fine.
Update: this seems to only happen from a CentOS 6 machine to a CentOS 7 machine. Maybe there is a missing library on 6 to display the new graphics in 7?