The BKF NV error is generally triggered by one of the following conditions:
Ensure the "Repartition" box in the tool's settings is only checked if you are performing a full firmware upgrade.
Open your SPD Flash Tool (Research Download or Upgrade Download). Load your firmware ( (gear icon) button. Navigate to the the following options: (if the error persists) and start the flashing process again.
To avoid encountering the BKF NV error in the future:
October 26, 2023 Subject: Troubleshooting NV Write Failures in Spreadtrum/UNISOC Based Devices