It may be that you are waiting longer than the allowed 30 secs between unlocking the car and starting it. The immobiliser kicks in at this point, hence seeming dead.
To overcome this (if you take more than 30 secs and it seems dead), just turn they key to the on position, press button on key fob once to override the immobiliser, then turn to ignition position to fire her up as normal.
Job done [emoji6]
Took me a few days to realise this too, so your not alone mate
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