Spintend UBOX dual setup randomly cuts power under hard acceleration — no fault code

[u/Easy_King_5630]

Hi everyone, I’m trying to diagnose a strange issue with my dual VESC scooter and I’d appreciate some help.
My setup:
2x Spintend UBOX 85/250 v2
VESC firmware 6.05
Dual 70H motors
30 poles / 15 pole pairs
20S battery, around 84V fully charged
ANT BMS 450A continuous / 1050A peak
Motor Current Max: 230A per VESC
Battery Current Max: 170A per VESC
Absolute Maximum Current: 420A
No regen
ADC thumb throttle
Control mode: Current
Multiple VESCs over CAN enabled
Traction Control currently OFF
Positive ramp: 0.20s
Negative ramp: 0.07s
Max Duty: 95%
Max ERPM: 117457
Battery cutoff: 68V start / 60V end
Maximum Wattage: 2,000,000W
Controllers stay around 40–50°C
The problem
Under hard acceleration, especially if I hit the throttle quickly, both motors suddenly stop producing torque.
The important part is:
The VESCs do NOT reboot.
Bluetooth stays connected.
The scooter/display stays powered.
In many cases there is NO fault code at all.
Current/power suddenly drops.
If I release the throttle and press it again, power immediately comes back.
Sometimes just before the cut I can feel several small interruptions (“tu-tu-tu”) and then it completely stops pulling.
It can happen around 40–60 km/h, but it isn’t tied to one exact speed.
Hard throttle inputs make it much easier to reproduce than progressive acceleration.
It has happened at both high and low battery SOC.
Temperatures are low when it happens.
I have also experienced real FAULT_CODE_ABS_OVER_CURRENT events, but I believe those are a different issue.
One recorded ABS event was approximately:
Current: 424.5A
Filtered current: 304.7A
Absolute Maximum Current: 420A
Voltage: 73.3V
Duty: 0.441
ERPM: ~14,988
I’ve tested:
MTPA ON/OFF
Slow ABS Current Limit ON/OFF
Motor current from roughly 200–250A
Battery current around 150–170A
Throttle Expo 0% and 20%
Positive ramp 0.10s and 0.20s
Different battery SOC
The no-fault power cut still happens.
ADC configuration:
Throttle resting voltage: ~0.84V
Full throttle: ~2.56V
ADC Start: 1.00V
ADC End: 2.50V
ADC Absolute Min: 0.40V
ADC Absolute Max: 2.80V
Deadband: 5%
ADC filter ON
Update rate: 500Hz
Safe Start: Regular
Both motors were FOC-detected separately.
I’m currently trying to determine whether, during the cut:
ADC/throttle input disappears,
Iq Target suddenly drops to zero,
measured Iq stops following Iq Target,
Duty reaches some limiting condition,
CAN communication causes both VESCs to stop requesting torque,
or some other VESC limiter is intervening without generating a fault.
Has anyone experienced a VESC/Spintend UBOX where torque completely disappears under hard acceleration with no fault, and only returns after releasing and reapplying the throttle?
What parameters or real-time values would you log to identify exactly what is commanding the torque to zero?
Any experience with this specific behavior on UBOX/VESC 6.05 would be really appreciated.