You can’t use the Test-ExchangeSearch cmdlet for monitoring or testing in Microsoft Exchange Server 2016. Monitoring application by running the Test-ExchangeSearch cmdlet causes the Powershell application pool to crash. In addition, the following error message is logged:
Log Name: Application Source: ASP.NET 4.0.30319.0 Date: DateTime Event ID: 1325 Task Category: None Level: Error Keywords: Classic User: N/A Computer: ComputerName Description: An unhandled exception occurred and the process was terminated. Application ID: DefaultDomain Process ID: 7332 Exception: System.NullReferenceException Message: Object reference not set to an instance of an object.