You have an Exchange Server 2013 organization that contains two servers named EX1 and EX2. EX1 and EX2 are members of a database availability group (DAG) named DAG1. DAG1 contains four mailbox databases. All databases are active on EX1 and replicate to EX2. You start an unplanned maintenance on EX1 and shut down EX1. You discover that the databases do not mount on EX2. You restart EX1 and the databases mount automatically on EX1. You need to identify what prevents the databases from switching over successfully to EX2. Which cmdlet should you run?