Meriva B - Rear doors not locking

[HorizonUK]

My father recently purchased me a 2012 Meriva B

It has an issue where the central locking will do 1 of 2 things:

- Locking the doors will engage all locks around the car except the rear locks

- Locking the doors will engage all locks around the car including the rear locks, but quickly after the rear locks disengage and become unlocked.

I have had a google around and most issues around the rear doors seem to involve warnings on the dash but I do not get any issues.

Any help would be appreciated.