Archiso doesn't work on non stock kernel
I've been having on and off issues when building ISOs with archiso and the other day when I was working on one I did a pacman -Syu before working but didn't reboot. I was running on the stock kernel at that point because the linux-ck kernel had not updated yet. My ISO built fine. Later that day I rebooted and was now running on the updated linux-ck kernel and suddenly the build process would simply die without any errors, even with the -v option. Right after installing all the custom packages, a dd output appears and then a mkfs.vfat version message appears and that's where it dies. Rebooting back to the stock arch kernel fixed the issue. I'm guessing it has something to do with hardcoded names or something like that in the build scripts.
Is this normal behaviour? I don't mind using the stock kernel on the ISOs I build but I figured I'd at least be able to build them on a different one.