Is the alarm led flashing when you are trying to start,if so its the immobilzer,if your keyfobs aren't working you will need the EKA code to start it,instructions on how to input code are in the vehicle handbook
The locks can do this,mine did,mine would unlock all doors except passenger front but once that door manually unlocked it would lock with the button no problem,replacement latch fixed it.
Also bear in mind that you only changed about half of the total amount of oil in the box and converter,if a change improved it then do it again before condemning the box.
I see your location is Norway,not sure on how strict the rules are there,here its a grey area as if a cat is fitted originally then it should be present at test but a lot of garages aren't bothered as long as the emissions limits are met.