Nvidia-smi is not detecting two card out of six

Hello! My system:

admin2@admin2:~$ lsb_release -a
No LSB modules are available.
Distributor ID:   Ubuntu
Description:   Ubuntu 18.04.5 LTS
Release:   18.04
Codename:   bionic

It was 6 cards on server

admin2@admin2:~$ lspci | grep -i nvidia
01:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
01:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)
03:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
03:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)
05:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
05:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)
06:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
06:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)
07:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
07:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)
08:00.0 VGA compatible controller: NVIDIA Corporation Device 2484 (rev a1)
08:00.1 Audio device: NVIDIA Corporation Device 228b (rev a1)

So that is result of nvidia-smi command

admin2@admin2:~$ nvidia-smi
Thu Aug  5 14:58:39 2021       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 470.57.02    Driver Version: 470.57.02    CUDA Version: 11.4     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|                               |                      |               MIG M. |
|===============================+======================+======================|
|   0  NVIDIA GeForce ...  On   | 00000000:01:00.0 Off |                  N/A |
|  0%   34C    P8    19W / 270W |      1MiB /  7979MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   1  NVIDIA GeForce ...  On   | 00000000:03:00.0 Off |                  N/A |
|  0%   27C    P8    15W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   2  NVIDIA GeForce ...  On   | 00000000:05:00.0 Off |                  N/A |
|  0%   29C    P8    14W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   3  NVIDIA GeForce ...  On   | 00000000:06:00.0 Off |                  N/A |
|  0%   28C    P8    10W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                                  |
|  GPU   GI   CI        PID   Type   Process name                  GPU Memory |
|        ID   ID                                                   Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+
admin2@admin2:~$ 

That is, it shows only 4 out of 6 video cards. All cards are on, they work. How can this problem be solved?
Moreover, I have exactly the same server next to it with exactly the same motherboard and cards and it shows 6 cards in nvidia-smi. Also on Ubuntu 18.04 lts, the nvidia-smi version is roughly the same (465.19.01 versus 470.57.02 on a server with 4 out of 6 cards). Can’t it be because of the version of the problem?
Thanks for answers!!

on other server nvidia-smi:

admin2@h1829658:~$ nvidia-smi
Thu Aug  5 14:36:13 2021       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 465.19.01    Driver Version: 465.19.01    CUDA Version: 11.3     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|                               |                      |               MIG M. |
|===============================+======================+======================|
|   0  NVIDIA GeForce ...  On   | 00000000:01:00.0 Off |                  N/A |
|  0%   27C    P8     7W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   1  NVIDIA GeForce ...  On   | 00000000:02:00.0 Off |                  N/A |
|  0%   27C    P8     7W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   2  NVIDIA GeForce ...  On   | 00000000:04:00.0 Off |                  N/A |
|  0%   28C    P8    11W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   3  NVIDIA GeForce ...  On   | 00000000:08:00.0 Off |                  N/A |
|  0%   30C    P8    12W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   4  NVIDIA GeForce ...  On   | 00000000:0A:00.0 Off |                  N/A |
|  0%   27C    P8     6W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
|   5  NVIDIA GeForce ...  On   | 00000000:0B:00.0 Off |                  N/A |
|  0%   26C    P8     9W / 270W |      1MiB /  7982MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                                  |
|  GPU   GI   CI        PID   Type   Process name                  GPU Memory |
|        ID   ID                                                   Usage      |
|=============================================================================|
|  No running processes found                                                 |
+-----------------------------------------------------------------------------+

Also upload here nvidia-bug-report.log from server
nvidia-bug-report.log (152.2 KB)