Is it normal to feel a bit of a shudder as the drive changes from 4 wheel drive to 2 wheel drive?
(around 40km/h)

Front wheel drive is on all of the time. Rear wheel drive is on when you pull away and decreases proportionately as you speed up but can re-engage if grip is lost. There is definitely something wrong if you get shuddering at the same speed but rear wheel drive doesn’t just turn off!

First change the fluid and filter, which might help. Mine also grabs as the AWD cuts in and out, but this develops slowly after a fluid change.
I'm going to run the calibration routine on SDD, when I can sort another power supply for programming required. 2009 Rimini Red SE TD4. Soon to be sold.
Hyundai Ionic 5 Ultimate on order.
Gone. 2006 Tonga Green i6 HSE.

I have never been able to notice the change from 4 to 2 wheel drive as speed increases, which presumably is they way it is supposed to work. Landrover - turning owners into mechanics since 1948

2014 Orkney grey Freelander SD4 GS.
2004 Zambezi silver Discovery 2 Td5 (Gone)
1963 Surf blue Morris Mini Minor Super de Luxe (my little toy)

I agree with Bob- I've had 3 FL2s - none shuddered Jules