The Luci message (initramfs…) means, that the actual flashing from the command you have shown has failed, as it is still booting from the temporary RAM-based firmware from the previous step, which is not preserving settings or changed password.
The following is guessing. Maybe you have one of the newer flash chips:
I am code-repository-dumb, so I do not know, whether the mentioned patch is already in the regular release already.
You might try to repeat both the „initramfs (!)“ and the „sysupgrade (!)“ step from your linked doc with the OpenWRT firmware files from the daily developer snapshot. as this will for sure contain the fix for the mentioned Toshiba flash chip. If this succeeds then the upcoming OpenWRT release v23 will be your friend