You have a mixed Exchange Server environment that has servers that are running Microsoft Exchange Server 2013 and Exchange Server 2016. When you run the Get-DatabaseAvailabilityGroupNetwork cmdlet in Exchange Server 2013 for an Exchange Server 2016 database availability group (DAG) object, you receive the following error message:
WARNING: An unexpected error has occurred and a Watson dump is being generated: Object reference not set to an instance of an object.
Object reference not set to an instance of an object.
+ CategoryInfo : NotSpecified: (:) [Get-DatabaseAvailabilityGroupNetwork], NullReferenceException
+ FullyQualifiedErrorId : System.NullReferenceException,Microsoft.Exchange.Management.SystemConfigurationTasks.Get-DatabaseAvailabilityGroupNetwork
This issue occurs because of a code change in Exchange Server 2016 that requires additional validation.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.