Time for an update...
Not long ago, Tesla Service replaced our car's charge port, charge port door, and the taillight enclosure just to the right of the charge port. Everything is working well now, and the Ranger who performed the service was proactive, considerate, and prompt. He emphasized that, with electromagnetic charge port doors like ours, the only thing that could mechanically prevent the door from opening on its own would be some kind of obstruction. In the absence of ice or other foreign material, slight misalignment of the charge port and surrounding panels and taillight could be the issue. In our case, the taillight enclosure was a problem.
In addition, the Ranger left us with a simple, plastic pry device, not unlike a bicycle tire tool. He recommended this keeping as a backup in case the charge port door sticks again, at least until we can contact Service.
Today, we are having our first snow and ice since the charge port was replaced. (I know, it's the middle of Spring and our temperatures are much warmer on average, but we're high in the mountains and a bit of May snow isn't all that unusual.) As the car had been plugged in overnight and we had rain that turned to snow, a pretty common occurrence when we have "winter" weather, there was a nice coating of ice around the charge port that prevented the charge port door from closing. So I loosened up the ice with a washcloth soaked in hot water, then chipped it off with a fingernail. There was still a slight crunching sound when I closed the charge port door, but I don't think any harm was done.
Perhaps the lesson is that we just have to be super careful using Tesla charge ports when there's ice present (or dirt, for that matter). They don't seem to be nearly as rugged as typical fuel doors on gasoline cars, or compared with the relatively giant charge port door on the Nissan LEAF. The charge port on the Model S/X is very elegant, but there seems to be a price to pay for that.
While I suppose it's too late to change this on the Model 3, I hope that Tesla will consider opting for a more robust charge port design on the Model Y, even if this comes at the expense of some elegance. As Tesla moves into the mass market, they'll find a larger percentage of their customers doing their overnight charging outdoors in the elements. I understand that the charge port can't be quite as simple as a traditional fuel door, though, because it has to be able to work autonomously.
