ssh -x timing out

Hi All, my main PC runs Fedora 29 I use X Windows to initiate programs on a Raspberry Pi 3
Quote:

ssh -X pi@10.1.1.91 "midori" &

This morning I upgraded raspbian on the Pi from stretch to buster. I achieved this by modifying source.lis and raspi.lis to reference buster rather than stretch then
Quote:

apt-get update apt-get dist-upgrade

After a reboot I am experiencing a few problems. The first is that the X windows session is not stable. It dies after a period of time. I can't figure out the actual period of time. I hear there is a ForwardX11Timeout setting which I can add to .ssh/config but I have never used this in the past. I had a look in journalctl but nothing jumped out at me.

Recapping then, any suggestions why a remote X windows session to a recently upgraded Pi initiated from Fedora would time out/get lost?