Comment 4 for bug 1858376

Steps:

(1)
Used: ubuntu-19.10-desktop-amd64.iso

(2)
Executed in chroot (No need for sudo, because user is already root!):
    apt update
    apt -y upgrade

(3)
45 combinations of vmlinuz and initrd were listed on the kernels tab in Cubic!
(This should have been 16, why 45???)

Accepted default option, i.e. the first option:
    vmlinuz.old
    init.img.old
    5.3.0-26
(The files vmlinuz.old and init.img.old, version 5.3.0-26, were also listed as the 2nd option. This is odd; they should be listed once only).

Clicked "Generate" button.

(4)
Encountered the error at 50% "update iso boot files". <--- ERROR !!!!

(5)
Clicked the back button.
Interestingly, this time I counted 59 combinations of vmlinuz and initrd.
(Was my original count incorrect, or did the number of options in the list actually change?)

(6)
Selected the last option in the list on the kernels tab:
    vmlinuz
    init.img
    5.3.0-18

Clicked "Generate" button.

(7)
This time, the FileNotFoundError error was NOT encountered.
ISO generation proceeded normally and was successful.