I have met a similar problem discussed here: https://devtalk.nvidia.com/default/topic/475012/?comment=3382808
I read the thread, but I did not find any useful information.
It seems OK with /dev/nv*:
crx-rx-rx- 1 root root 195 0 /dev/nvidia0
crx-rx-rx- 1 root root 195 255 /dev/nvidiactl
And I can get access to the GPU with root account. But if I run with non-root account, the GPU disappears.