Failed to initialize NVML driver. If gpu is disabled

[Dronte]

I have a dedicated nvidia gpu on my laptop that I enable and disable. nvidia (proprietary) driver is loaded and unloaded accordingly

My thinkfan.conf
has section

sensors:
  - nvml: 03:00.0
    optional: true

but when gpu is off and nvidia driver is offloaded, I get

ERROR: Failed to initialize NVML driver. Error code (cf. nvml.h): 28

on thinkfan start

[EnzephaloN]

Same here on ThinkPad P1 gen4 with nVidia A2000
I use nVidia-driver, Bumblebee and bbswitch.
thinkfan 1.3.1-1 on Arch Linux

sensors:
[...]
  - nvml: 01:00.0
    optional: true
[...]