Which Process Throws Error "StartImage failed: Load Error"?

I’m debugging a failed installation of systemd-boot on a multiboot Linux system (multiple instances of Ubuntu 20.04 & 22.04 in discrete partitions).

Sadly, the only consequence of

bootctl install

and other related configuration is that the system boots to the GRUB shell.

Exiting the GRUB shell occasionally takes one to either (a) yet another GRUB shell or (b) the systemd-boot menu (albeit with none of the configured boot entries).

Lately, after various tinkering, exiting the GRUB shell returns the message (with capitalization and spacing as in the original):

StartImage failed: Load Error

Google hasn’t heard of it, so the question is, which process is throwing this error?

Secondarily, would the error be a failure to load the kernel or initramfs?

Of course, any thoughts about how to get systemd-boot to observe its configuration also would be welcome.