PXE boot - unable to login

[LMM]

Hi all,
  I try to boot over the network (PXE boot) and follow the tutorial https://forum.pine64.org/showthread.php?tid=6814 with the Armbian image. After some hours to understand at the end that iptables was blocking the tftp connection I was able to boot but I cannot login : it is stuck when I enter the login or new password.
Do you have an idea of how to solve this issue ? root mount error ? NFS problem ?

LMM

I tried with both @ayufan  and @sigmaris  U-boot :

- Sigmaris U-boot stopped at booting level :

Code:

....
TFTP from server 172.21.200.1; our IP address is 172.21.200.31
Filename 'dtb-5.10.21-rockchip64/rockchip/rk3399-rockpro64.dtb'.
Load address: 0x1f00000
Loading: ######
         1.4 MiB/s
done
Bytes transferred = 75809 (12821 hex)
Moving Image from 0x2080000 to 0x2200000, end=3de0000
## Flattened Device Tree blob at 01f00000
   Booting using the fdt blob at 0x1f00000

- Ayufan stopped at login level