Let me ask you this question...
Where, in your mind would this microswitch be? On the keyfob there are two buttons, one locks all the doors, the other should unlock all the doors but only unlocks three ...
There are going to be a couple of different ways to lock & unlock all the doors without using the fob - there should be keylock on the outside of the driver's door and also a button or lever on the inside - what happens if you use those, do you get the same symptom, the same door not unlocking?
I'm going to guess, without any testing and as a matter of fact without ever seeing an S-Cross (they have never been sold here), that the problem occurs no matter which method you use and that suggests the problem is the lock actuator on that particular door.