The issue was low battery voltage triggering the Vmm protection. Even though the screen turned on, the voltage dropped under load at 1h10.

Let the device charge for 4+ hours (or use a powered USB hub). After that, flashed successfully with Spreadtrum Upgrade Tool R20.0.0001 .

: High-performance LTE support, including Cat-7 downlink (300Mbps) and Cat-13 uplink (150Mbps) .

if your unit is currently working well, as incorrect files can permanently damage (brick) the device. General Update Steps: Format a USB Drive

After the unit reboots, it is highly recommended to perform a to ensure the new "Vmm" configurations apply correctly without cache conflicts. Where to find Support

: Some units have a known bug where they periodically delete synced Google contacts.