Without seeing the OBDII codes it is kind of not helpful. If you can provide the Pxxxx codes there may be something common for these.

I did not re-read the thread from the beginning, but this is sounds like maybe a bad starter or bad ground somewhere.

Maybe you sorted these, maybe you need to check these again.

I would keep a Voltmeter in the vehicle and for the next no start situation verify the Voltage from the engine block to at least the under hood positive jumper terminal.

Ideally you would be able to measure the power to the starter, not sure if this is accessible or if you would need to put a temporary jumper on the starter positive terminal for testing.

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.