I found and followed this, rebooted and got the same result:
But don’t need to go there, here’s the conclusion which is what I implemented (exc. in /etc/ssh/sshd_config because /etc/opt/ssh doesn’t exist in my Ubuntu 18.04 install):
Oracle (internal) support came back with a fix that worked
"set X11UseLocalhost variable to 'no' in the file /etc/opt/ssh/sshd_config"
Probably SSHD daemon needs to be restarted.
I added the line: “X11UseLocalhost no” to /etc/ssh/sshd_config and rebooted to restart sshd although if you’re watching, you could do this with
% sudo service ssh restart
or
% /etc/init.d/ssh restart