Is it all the Fabias or just mine?

That in order to unlock all the doors except the drivers door, I have to hit the door just below the outside door handle? Just a slight smack with my hand the door unlocks.

Another way is to pull the door in from the inside, and you can hear the lock releasing (works better for the front passenger door).

Mine is a 2006 1.2HTP combi, I just bought it from original owner with 78k kms.

 

Is there anyway to fix this? What could be the reason?

You need to replace the locks, all three before you can't get a door open, then it gets MUCH harder to fix.