Comment 4 for bug 1954599

OK.
So the customized Live ISO does not boot.

You are doing two things:
    (a) Installing a new Kernel
    (b) Trying to change the Plymouth theme

Let's see if we can get (a)to work first.

I'll do the following test...

    1. Customize: ubuntu-18.04.1-desktop-amd64.iso
    2. Install kernel: 5.4.0-91
    3. Select the new kernel as (5.4.0-91) the ISO boot kernel
    4. Try to boot into the customized ISO

If there is a bug with Cubic while generating a new ISO with the selected kernel, this will help identify it.

Would you please conduct this same test on your end, so we can compare?

If this test passes, the next step will be to look at what happens when Plymouth is changed.