Loss power after tuning

Hi everyone,

I tuned a Lexus by reflashing the stock ecu. Everything was okey we tested the car in the same day and it preformed good , and the customer test his car the other day by racing his friend.

and it preformed great as he mentioned.

after few days he raced his friend again and informed me that the car lost power , because he lost the race

Is it possible that the car could loss power after few days ?

What can cause that ?

mechanical issue.

different weather conditions.

different fuel.

faulty sensor.

or the competition got faster. Lots of ways to lose.

Put the car back on the dyno to confirm the power loss (or not).

Thank you David for the reply .

yea i thought the same.

unfortunately it was street tuning so i can't see the power loss

but i thought that there is something im missing so i decided to ask