Picked my Macan up yesterday and I have the same problem. The speed limit function switches off at exactly the same place on road, about 2.5km (as the crow flies from my house). It switches back on at the same place. To test a theory I drove away from my home in a different direction and again it turned off after 2.5km. Could this problem by related to a geo fence which has been set up in the tracking software.
Car has been with Porsche Garage for 4 days. They have done a reset and recalibration of the innodrive but the Assistance system error persist sporadically. They are waiting further instructions from Porsche Germany but they are now saying it is likely just to be a software issue which could be fixed with an update… Still waiting for more info. Now they can‘t release the car until Porsche Germany agree it is safe …..