Failover readiness indicates whether or not there will be data loss on failover. If there will be data loss then check the Synchronization State. The database on this node could be behind time: in the process of synchronizing (Synchronizing) or Not Synchronized.
The Database State shows an error for databases in Suspect or Emergency states. It shows a warning for any other state that is not Online.
The LSN values refer to the Log Sequence Number.