Hey, I had the same trouble with my 16 wrx. Ended up taking it in and they changed the spark plugs/ checked them and rounded one off. Didnt sovle it but what ive started doing is waiting about 20 seconds before turning the car off and then when starting it waiting for the fuel pump (I think) to stop making that winy sound (so accesories on but not started yet) and when that stops start it then. Hasnt had a long crank since.
Hope that helps