Travelling to the Alps there appeared a red triangle with the error limited performance?
It happened again on return journey but resets when the car is stopped and turned off?
Land Rover garage failed to identify the issue, failing to trigger the problem in its tests.
Quite frustrating really, anyone got any suggestions?

 

Extreme elevation can cause problems with the electrical signals. The Engine Control Unit likes to see some of these signals in specific range. I'm guessing this is why a repair shop is failing to identify the issue. However, the red triangle with a message on the dash usually will store a fault within vehicle memory. Could be stored in a few different control units. Did the repair shop provide you will any fault codes that were stored?