Symptoms
Assume that you have mailboxes that have issues with the logical index in their mailbox database. When you try to use the move, restore, or repair operation on the mailboxes, the Store Worker process may stop responding randomly, and you receive the following error message:
System.NullReferenceExceptions" at "Microsoft.Exchange.Server.Storage.LazyIndexing.LogicalIndex..ctor
Additionally, the following event is recorded in the Application event log:
Log Name: Application Source: MSExchange Common Date: Event ID: 4999 Task Category: General Level: Error Keywords: Classic User: N/A Computer: XXX Description: Watson report about to be sent for process id: 20056, with parameters: E12, c-RTL-AMD64, 15.01.1261.035, M.E.Store.Worker, M.E.S.Storage.LazyIndexing, M.E.S.S.L.LogicalIndex..ctor, System.NullReferenceException, 1b58-dumptidset, 15.01.1261.035. ErrorReportingEnabled: False
Cause
This issue occurs because the lazy indexes of the mailbox can't be loaded successfully. This causes the Store Worker process to crash.
Note These lazy indexes are different from the context indexes that are built and maintained by the Microsoft Exchange Search service, as they are part of the Mailbox database.
Resolution
Exchange Server 2016
To resolve this issue, install Cumulative Update 9 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
