Dave you mention no fault codes or even the presence of an EML. I can understand the ECU being locked although you suggest it's been flashed then flashed back again. In any case it's inconceivable that OBD2 codes can't be read giving strong clues as a minimum to the root cause of your issue.

BTW I'm aware of low fuel pressure fuel sensor and high pressure fuel pump connections on GDI engine loom. I guess the latter could be some form of pump control but read it as electric fuel pump feed confused2

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone