820-02098 5V

Board had very very little corrosion in one corner of UG400 I replaced that and still same, DFU restore results in error 21.

PPBUS_AON - 12.0V
PP3v8_AON - 3.8V
PP5v_S2_MAIN - 5.2V
PP3v3_S2 - 3.2V
PP1V8_S2SW - 0V
PP1V2_S2 - 1.2V
PP1V2_AWAKE - comes up to 1.2V for a few seconds then drops to 0
PPVDD_ECPU_SRAM_AWAKE - 0V

U8100
PP1V8_S2SW_CLVR_VDDC1_LDO - comes up to 1.8V for a few seconds then drops to 0
PP3V3_AON - OK
PP0V8_S2_CLVR_VDDDIG - OK
PP1V8_AON - OK
PP1V2_AON - OK
PP1V5_AON_VCORE_MPMU - OK

U7700
PP0V72_S2_VDDLOW - OK
PP1V2_AWAKESW_BLC - OK
PP1V8_AON_SPMU - OK
PP1V2_AON_SPMU - OK
PP1V5_AON_VCORE_SPMU - OK

Did you replace UG400 with donor from same board and position?

I read its contents and re-wrote them on a new chip, I have done this on other boards such as 820-01700 with no problem when this IC go bad.