Comment 4 for bug 1880663

1. sudo apt update
2. sudo apt upgrade # to revert all what downgraded packages
3. do reboot test(battery mode) (3/10)
   failed at 2nd, 7th, 9th trial (4.15.0-1081-oem)
4. do reboot test, again(ac mode) (4/10)
   failed at 2nd, 4th, 7th, 10th trial (4.15.0-1081-oem)
5. sudo apt install shim=13-0ubuntu2 shim-signed=1.34.9+13-0ubuntu2 # downgrade shim only
6. do reboot test(battery mode (1/10)
   failed at 10th trial
7. do reboot test(ac mode) (6/10)
   failed at 1st, 3rd, 4th, 5th, 8th, 9th trial
8. do reboot test, again(battery mode) (6/20) (because it fails to boot up at 11th and 12th, I do 10 more reboot tests. BTW, it fails to boot up at 21st trial.)
   failed at 10th, 11th, 12th, 15th, 17th, 20th trial
It looks like downgrade shim doesn't help.

9. sudo apt install grub-common=2.02-2ubuntu8 grub-efi-amd64=2.02-2ubuntu8 grub-efi-amd64-bin=2.02-2ubuntu8 grub2-common=2.02-2ubuntu8 grub-efi-amd64-signed=1.93+2.02-2ubuntu8
10. do reboot test(battery mode) (3/10)
   failed at 3rd, 6th, 9th trial
11. do reboot test(ac mode) (2/10)
   failed at 2nd, 8th trial
Downgrade both grub and shim do not work.

12. disable TPM in BIOS(secure boot is off already)
13. do reboot test (4/10)
   failed at 3rd, 7th, 9th, 10th