Difficult to say based on to theories - obviously you need to inspect the BSI its to see if been effected by moisture,check that fuses and multiplugs/pins to the bsi are clean..they are quite prone to that on the circuit board aswell as solder breaks...obviosuly you need to get it plugged in lexia 3 to see and ensure or check for any stored codes or comms issues.. you could try this method below.if you havent done so already
Put the driver's window down, lift the bonnet and ensure all equipment is switched off.
Ensure all doors are closed and remove key from the ignition.
Wait for 3 minutes, disconnect the vehicle battery and wait 15 seconds.
Reconnect the vehicle battery, wait a further 10 seconds (do not open doors.).
Switch on the side lights through the driver's window.
Switch on the ignition and check system's functionality.
Hold lock button on key down for 10 seconds.
Remove key open & close door test central locking system.
Start the engine and complete the system's check.