Focus door lock failure

The symptoms you are describing certainly point towards an issue with the door contact signal. When the system doesn't receive the correct signal, it's like the car doesn't know the door status. A defective cable or plug connection would explain this. Do all the doors exhibit the same behavior, or is it just one or two?

It seems to be affecting all the doors at the same time, not just one or two. Does that point to a specific area I should investigate?

If all doors are affected, it strongly suggests a problem with a central point, like the wiring harness or the control module itself. While you could try tracing the wiring, given the complexity of modern car electronics, the most reliable approach is to have a workshop perform a diagnostic check. This will help to pinpoint the exact location of the fault, and thus prevent unnecessary repairs. The repair bill should amount to about 95€.

Thanks for the advice. I took it to the workshop, and they confirmed it was a defective plug connection as you suggested. All fixed now for 95€!