Found it, thank you, that output nails it. Your board is booting in safemode every time. The volume that stores your settings (overlay) is damaged (UBIFS error … LEB 16 scanning failed), so the kernel won't mount it, and the board falls back to keeping everything in RAM. So every reboot is a factory reset, not just upgrades. My guess is a power cut during a write, possibly around the v2.40.0 upgrade that went sideways.

Fix (whatever was in it is unreadable anyway; your settings are already gone):

ubirmvol /dev/ubi0 -N overlay
reboot

On the next boot the firmware creates a fresh settings volume, exactly as on first install. Then set your password, check mount | grep /mnt/overlay shows ubifs, and reboot once more: the password should survive.

If you want to try to rescue the old one first: mkdir /tmp/old && mount -t ubifs -o ro /dev/ubi0_2 /tmp/old. It probably fails the same way. Could you also paste dmesg | grep -iE 'ubi|nand|ecc|mtd' before you run the fix? I'd like to know whether the flash itself reported errors.