it is expected failure, may I know why you’re writing root file system partition directly?
please review all the partitions, $ ls -la /dev/disk/by-partlabel/,
you’ll see there’re several bootloader partitions that following with _b, which means it’s having redundancy to provides a safe Bootloader update and ensures that a workable Bootloader partition remains on boot storage during an update.
FYI, copy directly to a disk or partition would never work. The front of the disk would lose all of its partitioning information and no longer have any known partition scheme (old style BIOS versus new style UEFI…either would be destroyed).
In cases where you want to write to a partition (and not a filesystem on a partition) you’d use “dd”. Knowing your use-case example of what you want to do would be very helpful.