I had 2 systems, one I was able to start a remote gnome-terminal, (using ssh -YC <system name> gnome-terminal), the other failed with the assertion error.
One difference I found was in /etc/ssh/ssh_config
In the working system there was a line (added months ago to stop ssh from autologging out):
ServerAliveInterval 60
This wasn't in the failing system, I added the line and can now run remote gnome-terminals.
I had 2 systems, one I was able to start a remote gnome-terminal, (using ssh -YC <system name> gnome-terminal), the other failed with the assertion error.
One difference I found was in /etc/ssh/ssh_config
In the working system there was a line (added months ago to stop ssh from autologging out):
ServerAliveInterval 60
This wasn't in the failing system, I added the line and can now run remote gnome-terminals.