Hi All,
I've just joined to add my initial problems with the MMI.
I got my A3 Black Edition facelift model delivered last Monday and had the same issues as you all seem to be having - every time I came back to the car it wanted me to login again, it was set to a random radio station & the privacy and personal settings weren't being stored.
After a few frustrating journeys I decided to reset the MMI in the settings which took a while & was pretty nerve wracking; when I first set the car up after delivery I used the code from the scratch card that came with the keys & the QR code thing, so after the reset I decided to try using the My Audi login details instead and so far (touch wood) everything is working as it should and the various settings are stored.
I'm not sure if that helps anyone but I thought I'd share. The only thing I've done differently is not using wireless CarPlay, switching off wireless charging as it makes my phone ridiculously hot & I've also updated the map.
Interestingly my MMI software is on 4143 which seems to be the one people are having a bit more joy with & where I set the car up had 2 bars on the LTE display if that helps!