2004 Renault Kangoo Door locks

Hi, I recently bought a used Renault Kangoo van. The vendor told me that the side, sliding door 'Only sometimes' opens. The doors are locked/unlocked using remote key fob and the said door cannot be unlocked by standard key. Since I bought it, I have found the following:-

The door in question NEVER unlocks when all the others do using the remote and the interior unlock button cannot be raised manually from inside irrespective of whether the other doors are locked or not.

Shortly after locking or unlocking the doors using the remote control, all the doors sometimes start to randomly lock/unlock. This is VERY random. I can often hear it when I am 10 yards away after leaving the vehicle and it can happen several times after entering. It doesn't happen much when driving but sometimes happens when slowing down/stopped for traffic signals. As I say, this is totally random. I have just had over 2 days when it didn't happen at all, but then it started again.

When the doors start to randomly lock/unlock, the interior 'button' on the sidedoor will often rise to the unlocked position. This is the only time this door can be opened, and only then if I'm quick enough to do so before it locks itself.

I don't really need to use this door on a regular basis. I would be happy to manually unlock it from the inside when required. The main problem is the random locking/unlocking, which is obviously a security issue and VERY annoying.

Please help.

Ian