Kirin710 Fastboot command fail!
 

Before operation turn phone to TestPoint mode:
Turn off phone, then short TestPoint on phone pcb
and plug USB cable
Wait for device "HUAWEI USB COM 1.0" in Ports


Repair
New IMEI 1 : 860000000000098
New IMEI 2 : 860130000000098
New Bootloader code
New FB User Lock : UNLOCKED
Unlock downgrade/customization limitations
Reboot after repair
Selected Cpu/Bootloader - Kirin710_P1_V2
2021-05-05 02:33:17.688 Connecting to server...
2021-05-05 02:33:18.218 Connected!
2021-05-05 02:33:19.107 Find device COM14, handle 10964
BOOTLOADER selected to update:Kirin710_P1_V2
downloading file Kirin710_P1_V2_0.dtwork...
downloading file Kirin710_P1_V2_2.dtwork...
downloading file Kirin710_P1_V2_3.dtwork...
downloading file Kirin710_P1_V2_4.dtwork...
downloading file Kirin710_P1_V2_6.dtwork...
2021-05-05 02:34:31.708 Waiting for device REMOVAL/INSERTION...
2021-05-05 02:34:36.147 Device ready!
2021-05-05 02:35:18.763 Unlocking bootloader...
2021-05-05 02:35:18.767 Reading Certify data...
2021-05-05 02:36:43.279 Fastboot command fail!
Memo log saved to C:\Users\Online\Downloads\Compressed\HCU_378\Logs\ 20210505_023643_HCU_XloaderRepair_.txt

The same thing happened to me, the solution is when I sent you to fastboot, change the adb driver

If still have same problem make screenshot of device manager when your phone enters fastboot mode from testpoint.