Mini Cooper R56 Completely Dead

I drove mini cooper R56 for a very short distance for about 4 minutes, the whole car died completely. The battery was working fine, everything else seemed fine but the car died altogether.

Observations: All electronics systems seem dead, no light when I open the door, no unlocking by key FOB, no sparking when battery is jumped (eventhough battery is fine, tested several times, which indicates open loop)

Prior Issues: The car was hissing while acceleration due to spark plugs being worn out and I have already had them purchased but didnt get chance to replace.

To be honest this have happened once in the past but all electronics came back to life after 4 hours automatically but I couldnt diagnose what has happened.

Question: Could ECU have shut down all the electronics as a safety measure? Or could this be due to some electric trip somewhere in the circuit or could this be BCM?

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Update: Found someone else also experiencing exactly similar issue in Mini Forum, but unfortunately no valid solution so far.