Rock Pi 4A V1.4 4GB, uboot issues

Hello ,
I try modify the uboot environment and than use “env default -a” command.
Use the ‘Backspace key’ and the uboot will stuck and can’t do anything…

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U-Boot 2017.09-gfcf3aab (May 22 2020 - 08:04:45 +0000), Build: jenkins-rockpi-android-9.0-90

Model: Rockchip RK3399 Evaluation Board
PreSerial: 2
DRAM: 3.8 GiB
Sysmem: init
Relocation Offset is: f5be3000
Using default environment

dwmmc@fe320000: 1, sdhci@fe330000: 0
Bootdev(atags): mmc 1
PartType: EFI
boot mode: None
Load FDT from boot part
DTB: rk-kernel.dtb
select_boot_device_dtbo_id: boot device = 6:1
ANDROID: apply boot device dtbo,id=1
ANDROID: fdt boot device overlay OK
I2c speed: 400000Hz
PMIC: RK808
vdd_center 900000 uV
vdd_cpu_l 900000 uV
vdd_log 900000 uV
enable pcie power
Model: ROCKPI 4B
Rockchip UBOOT DRM driver version: v1.0.1
CLK: (uboot. arml: enter 816000 KHz, init 816000 KHz, kernel 0N/A)
CLK: (uboot. armb: enter 24000 KHz, init 24000 KHz, kernel 0N/A)
aplll 816000 KHz
apllb 24000 KHz
dpll 800000 KHz
cpll 24000 KHz
gpll 800000 KHz
npll 600000 KHz
vpll 24000 KHz
aclk_perihp 133333 KHz
hclk_perihp 66666 KHz
pclk_perihp 33333 KHz
aclk_perilp0 266666 KHz
hclk_perilp0 88888 KHz
pclk_perilp0 44444 KHz
hclk_perilp1 100000 KHz
pclk_perilp1 50000 KHz
Net: eth0: ethernet@fe300000
Hit key to stop autoboot(‘CTRL+C’): 0
=>
=> env default -a

Resetting to default environment

=> dd
(backspace key input and stuck…)