Not really JAMF related... but...
after starting a policy to upgrade to High Sierra I never regained control of the machine. When I get on sight to check it out I notice the boot progress bar is stuck stuck at around 90%.
Try reboot from Recovery and USB macOS install - same thing instantly happens. Impossible to boot from any device. Did the firmware update brick my machine? (Firmware password is on...)
iMac13,1
iMac Intel (21.5-inch, Late 2012)
