Comment 12 for bug 1848892

On a 19.04 system, I don't see the /boot/grub/x86_64-efi/tmp.mod file--so added during the upgrade.

Speculation:
--------------------
So, the problem might be related to signed versus unsigned kernels. The earlier kernel was probably signed. The new kernels from the upgrade are probably not signed. Can't test right now, but will follow up with another laptop. I will upgrade to 19.10 in the same way.

Using command:
  dpkg --list | grep linux-image
to list kernels lists past kernels not currently installed. Example on a 19.04 system:
...
rc linux-image-5.0.0-20-generic 5.0.0-20.21 amd64 Signed kernel image generic
ic linux-image-5.0.0-21-generic 5.0.0-21.22 amd64 Signed kernel image generic
ii linux-image-5.0.0-31-generic 5.0.0-31.33 amd64 Signed kernel image generic
ii linux-image-5.0.0-32-generic 5.0.0-32.34 amd64 Signed kernel image generic
ii linux-image-generic 5.0.0.32.33 amd64 Generic Linux kernel image

I only have the -31- and -32- kernels installed as is seen in the /boot/ dir:

-rw------- 1 root root 8785656 Sep 30 13:38 vmlinuz-5.0.0-31-generic
-rw------- 1 root root 8785656 Sep 30 22:58 vmlinuz-5.0.0-32-generic

See possibly related Bug #1788727:
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1848892