Store Worker process stops responding and returns "System.NullReferenceExceptions" multiple times per day

Symptoms

While 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. 

Cause

The process stops responding because of an unhandled System.NullReferenceExceptions exception that's generated multiple times per day.  

Resolution

To fix this issue, install the following security updates, as appropriate:

• Description of the security update for Microsoft Exchange Server 2019: June 13, 2023 (KB5026261)

• Description of the security update for Microsoft Exchange Server 2016: June 13, 2023 (KB5025903)