Galera cluster handshakes failed when applying new SSL certificate

After putting the new SSL certificate in the configured path, I tried to reload the SSL certificate of the MariaDB process using FLUSH SSL; with root user.

According to MDEV-25470, the command also triggers `socket.ssl_reload`. But I still receive the errors below when restarting the mariadb process:

WSREP: Handshake failed: tlsv1 alert unknown ca

WSREP: Handshake failed: tlsv1 alert unknown ca

WSREP: Handshake failed: tlsv1 alert unknown ca

WSREP: Handshake failed: tlsv1 alert unknown ca

WSREP: /home/buildbot/buildbot/build/gcs/src/gcs_core.cpp:gcs_core_open():221: Failed to open backend connection: -110 (Connection timed out)

WSREP: gcs connect failed: Connection timed out

I also tried to set `socket.ssl_reload` dynamically with `SET GLOBAL wsrep_provider_options='socket.ssl_reload=1';`. But I cannot find that option after setting with `SHOW GLOBAL VARIABLES LIKE 'wsrep_provider_options';`. And the errors still happened when I restarted the mariadb process.