The primary WAAE database was shutdown, but the Scheduler/App Server did not failover to the secondary database.
When WAAE loses the connection to one of the databases, it will attempt to reconnect with that database a configured number of times before failing over to single database mode. The default number of attempts is 5, but it can be set higher by modifying the DBEventReconnect parameter in the WAAE instance configuration. If the lost database comes back and the Scheduler/App Server are able to reconnect before exhausting those attempts, a failover will not occur.
There are certain database errors related to a db shutdown that can trigger an immediate failover. For example, for Oracle, if both the listener and the database are shutdown, the Scheduler/App Server will encounter an "ORA-12541: TNS:no listener" error on its first attempt to reconnect. This is one of the errors that would trigger an immediate failover. However, if the listener is not shutdown with the database, the Scheduler/App Server will encounter an "ORA-12514: TNS:listener does not currently know of service requested in connect descriptor" error. This error does not trigger an immediate failover so the Scheduler/App Server will continue cycling through the configured number of reconnection attempts.