Hi,
This is with the latest snapshot.
This is minor because it was being formatted anyway, but the issue is that I had created a raw unformatted partition outside of GUIX, but the GUIX partitioner tool was seeing it as possessing a filesystem of EXT4 already, when in fact it should have been blank. Maybe it is a trace of a previous partition that was in the space, but this is odd, it should not have detected a filesystem on a new blank partition.
This means it was not reading the partition table correctly.