Nope, I’m on Modern. Even tried switching to Legacy and back to Modern and tested again, still starts all mid air flights on AP. Try it man. Just start from say a random point around Nassau Bahamas (though I tested and it happens in Hawaii too). Don’t even set a destination, just go “Fly”. Trying going up or down and watch the trim autocompensate to fight your actions. Let go and watch the plane bounce back up or down wildly. Go to cockpit view and hover the mouse over AP and you’ll see the option to “Disengage Autopilot” - meaning it’s already on. Turn it off and back to normal.
*EDIT - tried also with the King Air and TBM930 and same issue exists, it starts the flight with autopilot engaged. Never had this before, always had to turn it on when I wanted to engage it.