I'm trying to move my installation from /dev/sda to /dev/sdb, I created the file system and changed the bootloader config in my operating-system definition to point to /dev/sdb and the file-system to use the correct UUID (previously it was using a label). First I tried to simply reconfigure my running system and then taking a BTRFS snapshot and copying that over the /dev/sdb1, but that failed. The exact error was GRUB not being able to find a file system with a given UUID, which matched the UUID of /dev/sda1. This error happened before GRUB loaded any of its modules, so I was dropped into a rescue shell. I thought this might be related to subvolumes, maybe I originally used the wrong config and the updated config was written to a different subvolume and GRUB doesn't recognize the default subvolume ID option on the BTRFS partition. I think this is a fairly critical error.
The error doesn't manifest when I run guix system init with the same config, so there is some (possibly un(der)documented) difference between guix system reconfigure and guix system init that makes the former rely on the state of the running system in a way that doesn't take into account the new configuration. Is this intended behaviour for some reason?