Just an update. Those nice folks at Marshalls Audi in Oxford, who all seem to be genuine Audi enthusiasts, contacted me a month ago to say there was a software update which should solve my MMI woes and restore the SOS function which was reporting a failure. Yesterday, my car went in for the day and was hooked up to whatever system they use to rewrite the MMI software.
When I picked the car up and drove out of the dealership, I got that grey box which says "Audi MMI User Details have changed. Apply new settings?"
Usually when that box appears, I "Ignore" it because you wait about 10-15 minutes with no MMI output while it seems to do Sweet FA, but yesterday I thought I'd give it go. The "Apply User Details Update" took about 10 seconds to do and then we were in business. As I passed the speed camera at Nuneham Courtenay, which usually coincides with an MMI reset, everything was fine. The dealer seems to agree that the issues with the MMI and SOS functions are caused by something to do with radio waves - whether it's 5G, aviation frequencies or something used by the RAF (we have a few RAF bases around and about these parts) no one can reliably say, but drivers have been reporting the concidence of MMI resets at the same spots over and over again.
Hopefully, this update will do the trick - I'll keep fingers crossed and report back.