I was getting a hill holder assist not available (or similar) message, which is bang on correct as mine is not fitted with one! I linked the issue to an intermittent starting problem, where you just get a 'click' after you press the start button. Second attempt near always worked. I traced the fault to a corroded earth lead from the battery to the body, which is held on with a 15mm bolt. I had to undo the bolt to see the corrosion. Cleaned with a wire brush until metal was clean, copper eased the bolt thread, refitted and coated with silicone grease. Been fine since.
I think the car, now 7 years old is nearing it's designed lifespan and issues such as this are going throw up unusual messages.