Use machine learning modules without enabling my discrete Nvidia GPU?

I cannot use some of the machine learning modules without enabling my discrete Nvidia GPU.

My setup:

  • Ubuntu 16.04 on a Dell XPS-15 9560 Intel i7 CPU with 8-cores,
  • Integrated IntelHD Graphics 630 (Kaby Lake GT2) card
  • Discrete Nvidia GTX-1050 card

To save power and reduce noise, I disable the discrete graphics card (using the Nvidia prime-select tool) .
In this mode, running NetTrain leads to the error:

LibraryFunction::libload: The function WL_MXGetVersion was not loaded from the file /usr/local/Wolfram/Mathematica/11.3/SystemFiles/Components/MXNetLink/LibraryResources/Linux-x86-64/MXNetLink.so.

Re-enabling the Nvidia graphics card and rebooting fixes this problem. However, the default mode of NetTrain is to run with 'TargetDevice → “CPU” ’ so surely I should not need to enable my Nvidia card to get this to work.