Skoda Kodiaq door lock issue

That does sound like an electrical issue, specifically with the door latch mechanism or its wiring. Given the symptoms, a defective cable or plug connection is plausible. Have you checked the fuses related to the central locking system? Sometimes a blown fuse can cause similar problems.

I haven't checked the fuses yet. Where exactly would I find the central locking fuse? Is it likely to be just a simple replacement or something more involved?

Based on your description, I am still leaning towards a wiring harness issue affecting the door latch. While checking fuses is a good practice, the intermittent nature and complete failure to lock/unlock points more directly to the door latch assembly or the wiring leading to it. A broken wire within the vehicle doors' wiring harness is a common culprit for electrical issues. If you are not comfortable diagnosing this yourself, I would advise consulting a workshop to avoid further complications with the electrical system.

Cheers for the advice. Turned out to be a dodgy wiring harness to the door latch, like you said. 95€ later and it's all sorted.