Thanks for this response @Entegy, and good to see Microsoft have recognised the NVIDIA dGPU problem with the Surface Book 2.
I should point out for this thread that my problem with using Adobe Lightroom 6 with Surface Book 2 also occurred before the 1903 update, just at a lesser frequency, and my understanding is that this is power related - my advice is to see how the problem differs when the battery is fully charged AND plugged into mains power - so hopefully this will help some.