Fiat Seidici: Intermittent Power Loss - Troubleshooting

First of all, have a wonderful day.
Here are the basic details of the vehicle: FIAT SEIDICI, manufactured on November 13, 2008.
Vehicle ID: TSMFYB61S00302358 Key No.: 8306/AAI Engine Code: D19AA 1.9 MultiJet Diesel
Okay, here's the translation:

"Now, regarding the problem: The customer occasionally reports a brief loss of power. I drove about 40 kilometers myself and didn't notice anything. Two days later, the woman called me again, saying the problem had reappeared – a brief loss of power, mostly when starting. I only read the error codes with a Gutmann MegaMacs 50, but no errors were stored."
Connectors and vacuum lines inspected externally.

"Has anyone had experience with these cars? Or does anyone know if Fiat has released any updates or anything like that? I'm not sure where to start because the car didn't exhibit the problem when I first got it, and as is often the case, I don't think it will start now, which is frustrating."

Thank you in advance. Best regards.

AGR failure.

Thank you for the feedback! How did you come up with that?