The car does do mostly short journeys, I wonder if that is a contributory factor? I am going to Scotland in it next month, I suppose if a long run might fix it, I'll know then. 2017 4.4 SDV8 Autobiography in black
2018 D300 SE Velar in champagne
1982 Rolls Royce Silver Spirit in green

If it has an extended warranty, then keep on at the dealer until the issue is resolved. If that means a new transfer box, then so be it

I'm beginning to wonder if some issues are temperature dependent ... as in ambient temp.

I've drained and refilled mine a couple of times over the last 12 months, and reset it with the IIDtool, and for the most part its been fine. However, I've noticed it slipping on 2 occasions. The first was after a long day on the motorways not long after drain/fill one ( done about Nov time ). I reset it at the end of the journey and it seemed fine since then.

The second ( after the second drain/fill - done again early winter time) has been over the last couple of weeks with the much warmer weather ... I'm noticing it now happening more often.

I'm now wondering if you re-calibrate it in the cold, that when it gets warmer thermal expansion occurs such that it begins to allow slippage and the juddering? Its clear that the unit it sensitive to the fluid it get, so could it be the temperature at the time it was calibrated ?

That would explain both my scenarios ... long motorway trip heats up the drive train. Better weather with markedly warmer temps than when it was calibrated has done the same too. V8 or else ...