It looks like this is a repeat of the previous issue with the shim (secure boot) loader. In the two boot logs you posted, the system is actually continuing on to boot the embedded OpenWrt from NAND because SHIM exits.
After that thread, the ‘manipulator’ script for Ubuntu was updated to force removal of shim. If your system was installed prior to that then apt will pull updates and reinstall shim as it did in the first update log.
The fix procedure (from recovery firmware) is:
mount /dev/nvme0n1p15 /mnt
cp /mnt/EFI/ubuntu/grubaa64.efi /mnt/EFI/BOOT/BOOTAA64.EFI
umount /mnt
/sbin/reboot
Once you regain access to Ubuntu, remove the shim-signed package:
apt-get --allow-remove-essential -y remove shim-signed grub-efi-arm64-signed
Perhaps mark these two so apt won’t try to install it again:
apt-mark hold shim-signed grub-efi-arm64-signed
The newer system firmware branch I am working on is compatible with shim so these workarounds won’t be needed after that. Until then this should ensure your system will continue to work after major updates.