I had the same issue a couple of years ago and VW assist came out and changed parts of the locking mechanism which seemed to sort it out until it happened again 6 months later. Second time after repeatedly trying to get it to latch shut, I started fiddling about with the inside door locking button thing and the inside handle which seemed to rest everything and it worked again. Roll forward another 10 months and it happened again when we were in France. That time, all I did was press down the locking button pull the inside handle as if to open and all was OK again. Several things emerge from my particular case. 1. That VW Assist already had parts on board tells you that it's a problem that comes up quite a lot (which is not unusual for VW) but they still didn't seem to have a handle on the root cause. 2. The very first time it happened, I could probably have sorted it myself as I did on subsequent occasions. 3. In my case anyway, I don't think it was anything to do with the door dropping.
Hope this helps.