[Christerart]

I have 2005 XC70 with a similar issue - except it's only the offside rear door that does what the OP describes - locks the door intermittently - in other words, not always.

I can't find any pattern to when this is happening - just now and then.

I unlock it from the driver's door lock/unlock switch and it unlocks and when opened and then closed it may - or may not lock.

Puzzling.