Mark, one more request for now. You say that you can boot up a non-Ubuntu kernel with the problematic microcode. Can you boot up one of those kernels and then verify the microcode revision with the following command:
$ sudo cat /sys/devices/system/cpu/cpu0/microcode/version
Please paste the results. Also, the kernel version would be useful. Thanks again!
Mark, one more request for now. You say that you can boot up a non-Ubuntu kernel with the problematic microcode. Can you boot up one of those kernels and then verify the microcode revision with the following command:
$ sudo cat /sys/devices/ system/ cpu/cpu0/ microcode/ version
Please paste the results. Also, the kernel version would be useful. Thanks again!