Picasso intermittently won't lock with fob or manually

Question

I've had my 2014 Picasso for half a year now. Twice in the last week, I've had an issue where the car will not lock. I have checked all of the doors but they are closed. There is no indication of an issue on the screens. Sometimes when pressing lock you'll hear a clunk but the doors don't lock and the side mirrors don't flash and close like they should. Other times it doesn't even register that the fob has been pressed. I understand that it could be the battery in the fob, however it won't lock with the manual key either. Today it at least made a clunk noise with the manual key but did not lock. The first time I ended up somehow setting off the car alarm. Both of these times I've given up on going shopping (both times happened in supermarket car parks) and have travelled on. When I've arrived at my next destination, the car locks first time with the fob. We booked it for a car battery test at Kwik Fit and the guy just told my husband that it wouldn't be the car battery so didn't check it and advised we should get an electronics diagnostic. I'd appreciate any ideas on where to focus before I start paying for garages to start investigating.