I had a similar situation today. guix gc removed the grub background png from the store. the one, that was used by /boot/grub/grub.cfg. the boot menu then had a black and blue background. rebuilding the configuration refetched the background image, but guix gc removed it again.
after rebooting and reconfiguring a few times 'fixed' it. I will report back, if I should be able to reproduce. -- GPG: 7FDE 7190 2F73 2C50 236E 403D CC13 48F1 E644 08EC
