Door Latch problems of the 2004 Porsche Cayenne

I have had problems with 3 of the 4 doors not operating correctly. My right rear door does not open at times from the inside or outside. The vehicle has been to the shop 4 times for repair and porshe has been unable to fix it. On 2 of the other doors, sometimes the outer door handles remain in the open position and do not retract after opening the door, often leading to the door reopening when you go to close it. In addition, sometimes the rear hatch does not unlock at times. I have been made aware by 2 Porsche dealerships that they have both had other customers with similar or related conditions. This is very serious and has the potential to lead to a very dangerous situation.