In the logs of the pod (mariadb-server-1) [4], I noticed issues related to mariadb tables but only in the failed pod.
This pod keeps rebooting and also stx-openstack applying keep fails each time.

2021-08-17 00:19:12,237 - OpenStack-Helm Mariadb - INFO - Recovering wsrep position: 2021-08-17  0:19:10 140357388367552 [ERROR] Could not open mysql.plugin table. Some plugins may be not loaded
2021-08-17 00:19:12,237 - OpenStack-Helm Mariadb - INFO - Recovering wsrep position: 2021-08-17  0:19:10 140357388367552 [ERROR] Can't open and lock privilege tables: Table 'mysql.servers' doesn't exist
 
[1] https://paste.opendev.org/show/808124/
[2] https://paste.opendev.org/show/808125/
[3] https://paste.opendev.org/show/808126/
[4] https://paste.opendev.org/show/808127/
[5] https://paste.opendev.org/show/808128/