Comment # 19 on bug 1206497 from Stefan Hundhammer

Since the Leap 15.4 installation ISO is not 232 GB large, but 4 GB
(openSUSE-Leap-15.4-DVD-x86_64-Build243.2-Media.iso), I guess you didn't use
the "imagewriter" program or a "dd if=... of=/dev/sda ..." command to write
that ISO to that disk, so some minor details are probably different from the
normal installation media. And that might just be what started this wrong boot
mode.