I had a similar problem with my 2018 1.6 DSG.
The autolock function only kicks in at a certain speed (10 mph?) - and then switches off again over a certain speed.
My car would constantly try to lock itself and fail and I would constantly hear the car trying to lock itself until I reached a certain speed. The problem was that when I parked my car the car would appear to be locked, but the passenger door would remain unlocked. Please check that your passenger door is locked when you lock the doors using the key fob!
I simply sprayed a liberal amount of WD40 into the lock mechanism and left it for a few hours and it fixed itself. I think as I never use the passenger door, it had simply seized up.
Another alternative fix is that your insurance might cover for you for keys and lock replacement. I actually had my keyring stolen (house and car keys) and they replaced the complete locks and keys without affecting my excess.