The car had a slightly inaccurate fuel flow sensor .They told the fia ,who said they should keep using it but they need to apply a 'recalibration factor' .Apparently it's a simple thing to do in the software

But the team still didnt trust the sensor and so DECIDED TO USE THEIR OWN INSTEAD. Thats where they went wrong.The fia even told them again during the race to use the fia sensor but the team kept using their own.

This is likely to be an ongoing problem between the teams and fia in future.Any calibration issues with those sensors effects how much power the car has.Any error or unreliability is a pretty big deal!