update by me, the original poster:
With respect to this particular laptop with two onboard GPUs (Intel 4k and nVidia), disable one or the other in device manager - displaylink usb adapters begin outputting video again.
To revise my earlier statement:
You displaylink cats have a problem with dual GPU machines and Windows 8.1, no matter how many times you ask the user to uninstall/reinstall/check PIDs/check lists of compatibility with USB3 controllers/etc.
Perhaps investigating why (gpu=2)=(displaylink=
) vs. (gpu=1)=(displaylink=
) would be a fantastic place to start debugging?
Thanks…we would all be really exited about that.