I received this problem recently when I logged into root on a machine.

X11 connection rejected because of wrong authentication

How did this problem happen? Here’s what I did.

ssh -X huyle@host
sudo su
xclock
X11 connection rejected because of wrong authentication

If I open xclock as a user, then X11 works just fine. As a result, I know that the server and client’s X11 forwarding is working.

A root problem

My .Xauthority and X11 credentials aren’t being passed over to root.

ssh huyle@host
sudo su
xauth merge /home/huyle/.Xauthority
xclock

xclock works, so all I had to do was merge my user’s .Xauthority to root's.