Pop!_OS expects the initramfs bootstrap file to be explicitly named "initrd.gz"

hello,

i've been tinkering with cubic to make a respin for the last month or so. simply an experiment with a few preinstalled creativity programs and some gnome extensions.

i started with ubuntu 20.04, but wanted to switch to pop os 20.04, with the hope that it is a ubuntu respin and would more or less "just work".

progress was really fast. live images were working perfectly. it was installing to virtual box on win/mac/linux without a hitch.

when i tried to install it to hardware it errors on install.

i tried to respin pop os without any changes, simply clicking through, and the same error occurs.

the error is

ERROR: configuring chroot error: error creating recovery partition: unable to open file at "/cdrom/casper/initrd.gz": No such file or directory (os error 2)
ERROR: errored while installing system: error creating recovery partition: unable to open file at "/cdrom/casper/initrd.gz": No such file or directory (os error 2)
INFO: Install error: error creating recovery partition: unable to open file at "/cdrom/casper/initrd.gz": No such file or directory (os error 2)

i'm wondering what i can change to fix this? i have tried both options of the boot kernal. but maybe there's something deeper i can look at.

other people have had similar errors without the respin chestnut, but there isn't a great amount of information.

thanks in advance!