Thanks, this was a good suggestion, but ultimately did not work. The same error is displayed booting from the main initramfs 
. Unsurprisingly, I’m still able to boot from the fallback initramfs…just worried about a kernel update breaking that too, or something.
Here was the output of that comand, if it’s relevant:
$ sudo mkinitcpio -g /boot/initramfs-5.4-x86_64.img
==> Starting build: 5.4.58-1-MANJARO
-> Running build hook: [base]
-> Running build hook: [udev]
-> Running build hook: [autodetect]
-> Running build hook: [modconf]
-> Running build hook: [block]
-> Running build hook: [keyboard]
-> Running build hook: [keymap]
-> Running build hook: [filesystems]
==> Generating module dependencies
==> Creating gzip-compressed initcpio image: /boot/initramfs-5.4-x86_64.img
==> Image generation successful
