LXD cluster : invalid client certificate

I have LXD cluster installed and its behave strangely today. When I check cluster list, it is appear that one of its member is offline.

+---------+---------------------------+------------------+--------------+----------------+-------------+---------+----------------------------------------------------------------------------------+
|  NAME   |            URL            |      ROLES       | ARCHITECTURE | FAILURE DOMAIN | DESCRIPTION |  STATE  |                                     MESSAGE                                      |
+---------+---------------------------+------------------+--------------+----------------+-------------+---------+----------------------------------------------------------------------------------+
| neptune | https://172.30.68.16:8443 | database-leader  | x86_64       | default        |             | ONLINE  | Fully operational                                                                |
|         |                           | database         |              |                |             |         |                                                                                  |
+---------+---------------------------+------------------+--------------+----------------+-------------+---------+----------------------------------------------------------------------------------+
| triton  | https://172.30.68.18:8443 | database-standby | x86_64       | default        |             | OFFLINE | No heartbeat for 15h12m54.799128025s (2023-09-04 15:48:03.216504734 +0700 +0700) |
+---------+---------------------------+------------------+--------------+----------------+-------------+---------+----------------------------------------------------------------------------------+

I check the LXD services in the offline node and it is running. I tried to check the debug message on the offline node with lxd --debug --group lxd and find invalid certificate error.

ERROR [2023-09-05T07:13:05+07:00] Invalid client certificate CN=root@neptune,O=linuxcontainers.org (a8190c3d03e0239a0ef02933996922c80f87bbee825a16d2c41fff3c458436ba) from 172.30.68.16:50874

I cannot run any lxc command on the offline node, whether its lxd service is run. It is hanging for long time and then exited with error Error: Get "http://unix.socket/1.0": net/http: timeout awaiting response headers

Can you run the following on the offline member to check if the certificate is still valid?

openssl x509 -noout -text -in /var/snap/lxd/common/lxd/server.crt

What do you see in /var/snap/lxd/common/lxd/logs/lxd.log