When a node is in the DONOR/DESYNCED state, it doesn't participate in flow control, so its data can get stale. Galera states are explained here:
A node's state can be checked with wsrep_local_state:
MaxScale's Galera Monitor treats nodes in the DONOR/DESYNCED state as unavailable unless available_when_donor is configured. This ensures that MaxScale does not route queries to a node that has stale data.
As far as I can tell, MariaDB Connector/J's load balancing implementation does not have a way to keep queries from being sent to desynced Galera nodes. Maybe we should add an option that would enable that kind of behavior?