Fixing X11 connection rejected because of wrong authentication
You get either “X11 connection uses different authentication protocol” or “X11 connection rejected because of wrong authentication”.
The thing is, this is a very generic error message that will take you to multiple very different fixes.
Many telling you to set a variable here and change a setting there.
In my case, it was because the SSH server had a configuration under /etc/ssh/sshrc
.
I found the answer here.
In my case, sshrc only had comments as I had stopped to use the file, so I just removed the config file and ssh -X user@server xclock
worked again.