And there are endless posts on debian raspbian and other forums about this, many with fixes that only work in very specific (unstated) circumstances.
In the end I just got out me Glasgow screwdriver and
stuck a new line in crontab to postfix the mess.
sudo crontab -e
and add the line
@reboot sleep 5 ; /usr/sbin/service rpcbind start ; sleep 10 ; /usr/sbin/service nfs-kernel-server restart