Allroad ESP, ABS, warning lights

[audidoody]

The ABS, ESP and Level warning lights are intermittently coming on on my 2004 allroad dash. . After a few seconds the ABS and ESP lights go out and leave the level warning light on for a few seconds as the air suspension drops from Level 3 to Level 2. Here's the strange bit. They only illuminate on a certain stretch of a certain road when the car is doing around 40mph into a long sweeping stretch that gently curves to the left. I took the car to an audi independent last week for a diagnosis but nothing showed up. I'd be grateful if anyone has got any ideas?