Following this bug [https://bugs.launchpad.net/ubuntu/+source/acpid/+bug/302452] might help fix it. I did try the mainline kernel mentioned there and still wouldn't reboot for me but I had a bunch of nvidia kernel modules errors at that point so maybe if i resolved those with that kernel it would work:
Following this bug [https:/ /bugs.launchpad .net/ubuntu/ +source/ acpid/+ bug/302452] might help fix it. I did try the mainline kernel mentioned there and still wouldn't reboot for me but I had a bunch of nvidia kernel modules errors at that point so maybe if i resolved those with that kernel it would work: