Does the car still pull as it used to?Just to make sure  your turbo is still ok.If so then i think its a call to the dealership as it can be anything even a lose connection maby or a sensor.

I have this on and off.Seems to stop working now and then when its cold/damp weather. last year at service they said they had fixed it and that it was a loose connection. Which probally means they did nothing.

How did you fix it ?
I am experiencing the same problem.

Don't want to sound daft but don't UK spec models just say "Sport" in them. Mine doesn't say shift up so is it a replacement gauge.

Yes my original on a 13 plate said shift up, the replacement says sport

This is quite an old thread but maybe my experience could help people who have this issue with the turbo gauge needle not willing to move.  I had this problem with my 595 (2016) last year and had it checked at the dealer's. He could not find the cause of it. Replacing would have cost around € 500.  To expensive, so I didn't change anything.  Except, one month ago, my battery died.  From the moment on the battery was replaced by a new one, the turbo gauge problem was solved as well.  I believe it was in a Dutch forum I've read that someone had the same experience.  So my advice is to first try a battery change. Good luck and greetings from Belgium, Marc.