Yeah, after the second (in your case 3rd) reboot, I no longer have ssh access and not enough access to the rest of the network to tell why. I was able to successfully reboot into the 9.1 kernel after the first upgrade/install. It was only the second that didn't work.
# freebsd-update fetch # freebsd-update install # reboot
# freebsd-update upgrade -r 9.1 # freebsd-update install # reboot
# freebsd-update install # reboot
remotely without any problems.