Symptoms
When a database availability group (DAG) is in production in Microsoft Exchange Server 2019, the Store Worker process stops responding. This causes the database to fail, and the mailboxes get quarantined every day.
The process stops responding because of an unhandled System.NullReferenceExceptions exception that's generated multiple times per day.
Resolution
To fix this issue, install Cumulative Update 13 or a later cumulative update for Exchange Server 2019.
