IMO, it's some kind of manufacturing quality issue. There is obviously some deviation between mirrors as they are manufactured. There should be a tolerance spec specifying what deviation is acceptable. There seems to be an issue with some mirrors on the edge of a spec (or maybe out of spec but poor QA didn't catch it, or Tesla needed to make cars for the end of the year rush and chose to accept parts out of spec) which causes the mirror to get stuck. Tesla is hoping they can fix that with a firmware update by driving the motors harder. In my case my mirror also has a problem of glass surface position save/restore not working at all, something Tesla is also hoping to fix with a firmware update. Somehow "hope" has become Tesla's strategy go-to lately. *sigh* The problem is, nobody seems to know when this update is coming and what it will fix. Maybe the mirror issue is rare enough that it doesn't get any priority with all the EAP hoopla. If that's the case it won't be fixed by end of this month, at which point I will just ask for a mirror replacement - if they cannot fix it within more than a month that suggests to me they'd rather pay for mirror replacements. Since not all cars are experiencing this issue, seems eventually I should end up with a mirror that will work.
To add to this, all cars don't get updates at the same time. Our older car got 2.52.22 a couple of nights ago, but the new one, which has the mirror problem, did not. It could be that they haven't figured out how to provide regular cruise control (the new car doesn't have EAP enabled and we know it was an issue on the first 1000 cars), or it could be because the new car doesn't automatically connect to WiFi when it's parked in the garage. If I click the WiFi icon, it "initializes WiFi" for a while and the suddenly it's all connected automatically. It also automatically connects after main screen manual reset, but not if you drive it and come back home. WiFi signal strength is almost full, so that's not the issue. Also, the other Model S in the same garage connects every time.
This is my 3rd Model S, and I gotta say, the initial quality seems to be going down every year. My 2013 had the least issues, 2015 had some more, 2017 is having yet more issues. None of them are making a car undrivable, but when you spend this kind of money for a car, it should come in working order, including non-critical functionality like mirror folding or position restore, no? The only thing that makes up for it is Tesla's excellent service - Tesla's saving grace really. This strategy of having customers do QA and having SC's fix things is not going to work come Model 3 volumes.