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Hi Mark, the update would only take effect when it goes to a hotspot, the network side of things is unaffected so it seems you have a different issue.
The version of stretch shouldn't make a difference, i have various pi's on different states of Jessie and stretch and it works ok on them all. The image i tested it on was the latest one, with updates to Thursday.
If you have no network then at boot there is something else going on.
Check /etc/dhcpcd.conf that the line is interface wlan0 and not interfaces wlan0, check your wpa_supplicant.conf file.
Are you able to make any changes if you have no network and not on a screen?

Even with the authotspot.service disabled so the script is not used you will still have network and ssh at boot. If you can check sudo systemctl status dhcpcd for errors.
You could check the logs in /var/logs for issues. Try messages and syslog. Try grep -i dhcpcd /var/log/syslog

If you do the removal section and disable autohospot and undo dhcpcd.conf then see just try to get your network back. Then re-enable them and see what happens

Let me know what results you get.