I doubt the FIAT examiner has shown nothing. Either the Service center doesnt have lates FIAT examiner version or he has not examined it properly. There are two types of error, one is general and other is blocker, the ECU records all sort of unwanted happenings. Even the "Low Engine Oil" error that sometimes user gets when the car stops abruptly due to poor clutch release etc. Examiner allows deletion of the general error logs on a single click, but the blocker error log cannot be deleted unless the issue is resolved. I am very sure there must have been log details of engine failure (improper shutdown) logged, its possible the actual reason might not have got logged but shutdown would have been surely logged. It even records if a sensor fails temporarily (lose connection, one has to go through the chronology of log to find what would have happened. If the service guy runs a check error on examiner, he will get "no error found" if that issue is not currently in active state. Which means that there are fair bit of chances that there has been some lose connection which breaks the connection in a certain drive condition. And since its not complete mechanical failure, it could have not been detected in ECU check.