Hi. I ran into this recently kickstarting both 5.5 and 6.2 hosts. Kickstarts worked one day and the next the bootloader wanted to be on the usb key, odd. This is was an example of what worked for me with 5.5 where the usb key was consistently seen as sdb. Both at their respective parts in the preamble section of ks.cfg.
#stop writing bootloader to usb
bootloader --driveorder=sda,sdb --location=mbr
#stop erasing my usb stick
General support questions including new installations