Customer could no longer connect to mariadb databases (galera cluster) after upgrading from MaxScale 2.4 to 2.5.
*Workaround/fix *: After numerous tries with different versions >2.5.x incl. 6.3 of maxscale, I was able to reproduce the customers issue and resolve the issue by removing/commenting the following from their maxscale.cnf: max_slave_replication_lag=1s. No matter what value was set, if max_slave_replication_lag was set it failed.
Note: this only fails with: module=galeramon, there are no errors with the mariadb client to connect and execute a query with module=mariadbmon.
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MariaDB [(none)]> show databases;
ERROR 2006 (HY000): Server has gone away
No connection. Trying to reconnect...
Connection id: 2
Current database: *** NONE ***
ERROR 2013 (HY000): Lost connection to server during query
Jun 6 20:47:14 localhost maxscale: Could not find valid server for target type TARGET_SLAVE (COM_QUERY: show databases), closing connection.#012#012name: [Node1] status: [Slave, Synced, Running] state: [NOT_IN_USE] last opened at: [not opened] last closed at: [not closed] last close reason:  #012name: [Node2] status: [Slave, Synced, Running] state: [NOT_IN_USE] last opened at: [not opened] last closed at: [not closed] last close reason:  #012name: [Node3] status: [Master, Synced, Running] state: [IN_USE] last opened at: [Mon Jun 6 17:47:14 2022] last closed at: [not closed] last close reason: 
Jun 6 20:47:14 localhost maxscale: Routing the query failed. Session will be closed.