GPUs disappear from the nvidia-smi list

I have a 4-GPU GeForce GTX 1070 Linux Server.
Software environment is NVIDIA-SMI 418.39, Driver Version: 418.39, CUDA Version: 10.1, CentOS Linux release 7.5.1804 (Core).

My problem is that some GPUs will disappear from the nvidia-smi list without any warning.
The problem is solved after I restart my server.
For example, nvidia-smi could find 1 GPU only.

$ nvidia-smi -L
GPU 0: GeForce GTX 1070 (UUID: GPU-d68c8435-7626-4025-23a1-f3c2d0e1ee7f)

$ lspci| grep -i nvidia
19:00.0 VGA compatible controller: NVIDIA Corporation GP104 [GeForce GTX 1070] (rev a1)
19:00.1 Audio device: NVIDIA Corporation GP104 High Definition Audio Controller (rev a1)
1a:00.0 VGA compatible controller: NVIDIA Corporation GP104 [GeForce GTX 1070] (rev a1)
1a:00.1 Audio device: NVIDIA Corporation GP104 High Definition Audio Controller (rev a1)
67:00.0 VGA compatible controller: NVIDIA Corporation GP104 [GeForce GTX 1070] (rev a1)
67:00.1 Audio device: NVIDIA Corporation GP104 High Definition Audio Controller (rev a1)
68:00.0 VGA compatible controller: NVIDIA Corporation GP104 [GeForce GTX 1070] (rev a1)
68:00.1 Audio device: NVIDIA Corporation GP104 High Definition Audio Controller (rev a1)

nvidia-bug-report.tar.gz (1.73 MB)

Please run nvidia-bug-report.sh as root and attach the resulting .gz file to your post. Hovering the mouse over an existing post of yours will reveal a paperclip icon.
https://devtalk.nvidia.com/default/topic/1043347/announcements/attaching-files-to-forum-topics-posts/

Thanks your reply. I have add bug report on my last post.

Please set up nvidia-persistenced to start on boot and make sure it is continuously running.