Symptoms
In Microsoft Exchange Server 2019 or Exchange Server 2016, you find the execution time for Exchange PowerShell cmdlets becomes longer than expected when it is compared to Exchange Server 2013, especially the cmdlets related to recipient objects, such as Get-Mailbox and Get-Mailuser.
Cause
There’re too many AD calls caused by the leftover code that was introduced for Exchange online.
Resolution
To fix this issue, install one of the following updates:
For Exchange Server 2019, install the Cumulative Update 4 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
For Exchange Server 2016, install the Cumulative Update 15 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
References
Learn about the terminology that Microsoft uses to describe software updates.