Ford Mondeo: Won't Start After Empty Tank?

Ford Mondeo 2.2 TDCi, year 2008.
The vehicle broke down while driving on the highway. The fuel tank was already on reserve. However, the display still indicated an estimated remaining range of 20km. When attempting to restart the vehicle, the fuel gauge only showed a remaining range of 2km.
ADAC determined that the fuel tank was actually completely empty, and therefore the car likely ran out of fuel.
The vehicle was refueled by the ADAC. Unfortunately, multiple attempts to start the engine were unsuccessful.
After the vehicle was towed to the workshop, the mechanic immediately checked to see if fuel was reaching the high-pressure injection pump. According to the workshop, this is the case. The mechanic also didn't have an explanation as to why the car wouldn't start despite having been refueled. He said that this needs to be investigated further.

What could be the cause?

Thank you very much.

Regards, TurbochargedDiesel.

Cause: Air.
Solution: Bleed.

If you're unlucky, the pump might be damaged because the parts are relatively sensitive. They are lubricated by the diesel, and if there is no more diesel and endless attempts are made to restart it, it can easily get damaged. But you still have a warranty on it .
Have you checked the manual?

Thank you for the quick response.

You are right about the warranty , but unfortunately, that doesn't change the fact that the workshop itself doesn't know what's wrong.

It initially seems logical that a lack of lubrication is the cause, but wouldn't the system shut down if the fuel pump doesn't receive any diesel, in order to protect the high-pressure pump?

Quote:

But won't the system be shut down if the fuel pump doesn't receive any more diesel, to protect the high-pressure pump?

Correct. The starting of the engine will then be prevented.

And what was it ultimately? As far as I know, in these cases, more than just one canister of fuel needs to be added. For safety reasons, the engine shuts off and remains in a "limp mode" until there is sufficient diesel fuel available.

Oops.