I posted bug #223081 - https://bugs.launchpad.net/ubuntu/+source/linux/+bug/223081 - with what seems to be he same problem. And it rather looks like the machine is overheating, with the kernel failing to contain the temperature rise and resulting in the system freezing. That also explains why a reboot directly afterwards is failing, since the system activity at reboot causes the hot machine to overheat again.
I posted bug #223081 - https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/223081 - with what seems to be he same problem. And it rather looks like the machine is overheating, with the kernel failing to contain the temperature rise and resulting in the system freezing. That also explains why a reboot directly afterwards is failing, since the system activity at reboot causes the hot machine to overheat again.