Had the same issue and been in for diagnostics. Don't use start/stop any longer but had a near miss on a roundabout when the engine stopped. Audi say nothing wrong with car and that it will stop if the engine RPM falls below 775. Now had an even stranger explanation bearing in mid this is a manual car.
"The engine is designed to switch off while driving if you are coasting, running downhill or approaching a roundabout ect where the engine is not required. This is why the vehicles now have a 48 Volt system to provide power to the steering, brakes, air con ect while driving without engine power. The grey stop start symbol in the display is just telling you it has switched the engine off as it is not needed right now. It is perfectly normal."
Are they really saying that this car has a mind of its own?