While updating my base kickstart for CentOS 8.1, I noticed it won't auto-load from a USB device. I'm testing in a VM, but usually add a USB drive for the ks.cfg because my kickstart skips USB drives when picking where to install. If I leave the drive a virtio, or make it a CD, it works.
I found https://bugzilla.redhat.com/show_bug.cgi?id=1770969 which then references a RHEL-subscriber-only solution.