if I remember rightly there was a technical issue with the transmission software of some 7 series relating to a very harsh second to first down shift ie when coming to a stop. The rectification for this was simply a software update. You will need to contact your dealer to confirm this and have the fault codes read from your vehicle. The worst case scenario would be a mechanical transmission fault but I would consider this unlikely as I cannot personally recall ever changing a transmission on this model.
An OBD reader is always useful but not so much in this situation. The tech at your dealer will read the fault codes from your transmission ECU and then use these fault codes to search on the BMW technical website (Puma) for any current issues. If the cause is a software issue then i'm afraid it can only be rectified by either your dealer or a very very well equipped specialist.