Hello and welcome to JustAnswer!
Do you have a test light to do some testing or are you just looking for possible causes?
Are these power sliding doors or manual?
If you unlock the doors by hand are the lock buttons stiff to move?
The first thing you would want to do is unlock them and relock them by hand to see if they move stiffly. If they do then the lock solenoids are bad and will need to be replaced.
If they feel ok then some electrical testing will need to be done to see what is going on. There are two main electrical causes for this, either broken wiring or bad lock solenoids. If you open the doors and look in the lower opening you will see a wiring harness inside a black plastic chain. These wires flex each time the door moves and can end up breaking. If you were missing power and ground to the lock solenoids then the problem is likely in this harness.
If you did have power and ground to the lock solenoids when actuated but they won't work then they would need to be replaced.
The wire strands will break inside the wire's insulation, so you can't always visibly see a break.
The lock solenoids are mounted to the door latches in the back of the doors.