I have a old R plate Sharan which does the same sort of thing.

If you start it from cold and keep driving it you have no problems. If you go to re use the car within about 90minutes the turbo will cut out around 3000rpm, like yours if you turn it off and start it again the turbo works until you get to 3000rpm again.

If you leave it more than 90mins 99.9% of the time it don't cut out

I just live with it as nobody can find out what is wrong.

Steve