To start with noticed rear passenger door would not open from outside when unlocking all other doors. But you could open it OK from the inside handle.

Having done this again recently, I later noticed that it wasn't locking, and cannot get it to lock.

Saw a few similar topics on here, so removed door card, got part No. 5TA839015L for locking mech, and ordered a replacement from eBay (£50) Swapped mechanism OK, but have exactly the same issue.

Only thing different I now notice is I get an electric child lock warning on dash at startup, and cannot enable the child lock on the rear passenger door (light doesn't come on) like it does on the rear right door.

Not that I have ever used the rear child locks or need to, but didn't have the warning on the original lock?

When I lock / unlock the car, you can feel the lump of the lock mechanism with your hand on the door on all but this rear passenger door.

Is it likely to need a code scan / clear / reprogram from a dealer to resolve, or could it be wiring loom issues?

I saw in one thread, there was mention of resetting by disconnecting battery overnight or similar - is this worth a try ?

Grateful for any advice which may help resolve the issue.

Most people will advise to check your battery is okay, as in, does your start/stop work without issue?

Door lock issues are a common fault, so it could just be that you’ve been unlucky with the replacement…I take it that you bought a 2nd hand part?

If you went with the exact same part number, it could be that the part you bought is about the same age as the one that’s gone faulty.

When I changed my rear door lock, I asked on here and a helpful forum member was able to give me the correct part numbers (there are many variants)

I chose to look for the “latest” part number and found a 2nd hand lock on eBay from a 1 year old Taigo that had done very little in the way of mileage.