Looks like you are right.
Did not want to modify uboot to make it understand f2fs , so i had to move /boot to ext4 and keep rest of / on f2fs.
Now it boots.
Thx for help.
Built image with such flags:
Etched img to sdcard and SBC has no response on power up.
U-boot log:
OS boots normally if I use ext4, but would like to stick to f2fs.
Btrfs or f2fs used to work if I used 7 months old armbian-build git checkpoint but not any more.
Anyone else had similar problems?