r316677:EFI boot failure: Can't load kernel

[Hartmann, O.]

After today's update to r316677, some UEFI boxes (Fujitsu Celsius M740
XEON) reject to boot properly. They die immediately after
loading /boot/loader.efi and jump into loader prompt:

[...]
\
can't load 'kernel'


I had to investigate with an USB flashdrive the filesystem, but
everything seems to be properly in place and installed.

I need advice how to revive the system after this.

Thanks in advance,

Oliver