I have repeated this exact same process twice just now and got the same result both times:
1. Flash the latest m2p stretch image to an SD card for use in a Raspberry Pi Zero W
2. Configure the wifi network using Access Point mode
3. Disable desktop mode, change video memory to 16mb, disable bluetooth, set Pi and Root password, disable autostart Shairport, change timezone to America/Los_Angelas, enter email address for license, reboot
4. Update max2play using the button in the web interface, reboot
5. Using ssh, do sudo apt-get update then sudo apt-get upgrade, reboot
On this reboot, the Pi Zero fails to boot, displaying this message on screen