Cars are very complicated these days. This sort of post-new-car experience isn’t that uncommon. Good ideas above; I expect the remaining problem will be fairly quickly resolved by the mechanics at the dealership. Or they may need to ask the manufacturer’s engineers for help too. You are noticing the mechanics seem puzzled, and they probably are, given the “computers-on-wheels” nature of newer cars. But the dealership mechanics have all the tools and diagnostic equipment necessary to solve tis issue. I doubt any other shops in your are would be able to do as well. This may take some patience on your part. Try to maintain a constructive relationship with the dealership shop. Let them know you’ll allow them to keep your car and drive it themselves as their daily driver to aid the diagnosis. Best of luck.
In the way of misery loves company …