BATT_WATT_MAX not working properly will cause crash from lack of power

I have matek h743 wing with a 5s setup in AR900 wing . 5s will cook the motor if applied for too long .
I set BATT_WATT_MAX to 400 watts . Since this is supposed to come on gradually i still get 100% for a few seconds before throttling occurs based on above parameter .
This is all on bench with motor on thrust stand . For the first pull the command works as intended . After a few seconds the motor begins throttling to stay under 400 watts max . The setup can draw 32 amps at 100% .
The problem is the second pull and subsequent pulls it throttles the motor WAY too much .
Im lucky to get 7 amps on second pull , 3 amps on third , 1.5 on 4th . less and less with each pull . its not the battery .
With each successive pull the max current gets less until im lucky to get 20watts of power out of motor .
When I shut off BATT_WATT_MAX I go back to 100% throttle . Im talking seconds here so the battery is not drained out from one pull to the next .
Nothing is changed from one pull to the next . I give full throttle then back to zero , full throttle then back to zero
there is something wrong here ! Luckily I discovered this on bench as the plane would have quickly crashed from lack of power ! This command does not work .