Gasly finished third on track on June 7 but was demoted to seventh when two five-second penalties for pit-lane speeding were applied post-race, with fellow Frenchman Hadjar promoted to third.
That decision was overturned after a right to review on June 12, stewards accepting Renault-owned Alpine's evidence that there had been a timekeeping error.
The FIA's International Court of Appeal then met last month to hear a McLaren and Red Bull challenge, with the verdict issued ahead of the Italian Grand Prix.
Alpine dubbed the final verdict disappointing and unjust in an official statement, but accepted the decision.