Door locks rear door behind driver

Assuming that you have electronic locking system as you described that will unlock all the doors....

Each door has a electrical means and a mechanical means of unlocking and locking the door. Similar to how pushing down the mechanical button or switch on one door manually unlocks or locks it, using a key in the door does the same manual mechanical lock or unlock. When you go to another door, only that door is manually unlocked when you twist the key. All the other doors are triggered to unlock when you twist the key using a different electronic system that uses a motor to electronically move or twist the button/switch which will lock or unlock the doors.

The electronic mechanism in your door handle that won't lock with the rest is most likely damaged, worn out, needs replaced. Depending on the model of vehicle, these can be fairly cheap to replace (probably anywhere from $5-50) and will take about an hour or so to replace depending on the model of the car and skill of the repairer. You should be to easily find this part once you've identified it on Amazon, NAPA, or other online stores.