@greentea1 There has been a patch added to Armbian’s U-Boot sources which seem to be related to your eMMC boot issue: odroidn2: u-boot: fix eMMC stability · armbian/build@5c15e3f · GitHub
Would you mind to test this:
wget 'https://dietpi.com/downloads/binaries/testing/linux-u-boot-odroidn2-current.deb'
dpkg -i linux-u-boot-odroidn2-current.deb
source /usr/lib/u-boot/platform_install.sh
# Unmute output/errors
eval "$(declare -f write_uboot_platform | sed -e 's| > /dev/null 2>&1||g' -e 's|status=none|status=progress|g')"
write_uboot_platform "$DIR" "$(lsblk -npo PKNAME "$G_ROOTFS_DEV")"
But if it fails, you would need to flash the other U-Boot binary from another Linux system, to make it boot again 
.