This may be an issue: “fuseblk”.
During a flash a sample rootfs is copied in to the “rootfs/” subdirectory. Various drivers are updated to be the NVIDIA-specific hardware-accelerated version. Then the bootloader directory gets an image the size of the final rootfs there, and it is this image which is flashed. If the files in the “rootfs/” subdirectory do not correctly preserve file permissions and types, then the resulting image has those same issues. Boot fails as soon as root permission is required, but in which root does not have the permission.
Some file system types are not capable of preserving permissions because they are not native to Linux, e.g., NTFS and VFAT have no knowledge of root since there is no such thing in the the Windows world. I am thinking that your fuseblk and/or any actual storage underlying it is not a native Linux file system type. Normally this would be ext4. If you try to flash from a Live DVD or similar, then flash will succeed, but actual operation will always fail. Can you run this from a real ext4 formatted partition? There is no possibility of success without a file system preserving Linux’s full permission setup.