It could be that the coffee machine has a mains filter (including capacitors) across the power input before the on/off switch, and the act of plugging it in creates EMC interference (a spike) that upsets the cooker hood controller. I don't think it's necessarily anything sinister.
The options are:
Put the coffee maker somewhere else on a different circuit.
Leave it plugged in!
Put an interference suppressor on the power input to the cooker hood (or at least try one - it may or may not help!)
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