Tried to access the sites I had set up via https://myurl/xxxx and they were not working today.
Checking the /etc/nginx/sites-available I could see that an update had been done on the 23 Oct and further checking shows this seemed to be to the openmediavault-webgui.
Checking the backup made a few weeks ago showed that the
listen [::]:80 ipv6only=off;
line had been changed to
listen 80;
and
listen [::]:443 ipv6only=off;
changed to
listen 443;
changing back seems to fix everything!
Not sure why right now.
The net result of this was that the 2nd server block I had for myurl was being ignored by NGINX.
Looks like I might need to fix this regularly from now on which is a bit of a pain!