For example, when trying to add a user for permission to another archive or add a user as a target for Provisioning, the VAC may only show 100 out of thousands of possible users in Active Directory. In the image below, notice that the list is pulled all the way down but is only displaying names starting with A, listed in alphabetical order.

***This issue is independent of the EV server's Operating System version.***
Microsoft updates that made key changes to the NetQueryDisplayInformation API in Windows 2016 and 2019, and when these updates are applied to the Domain Controller that serves requests from EV to list users, the issue is seen.
For Domain Controllers on Windows 2019, the update is found here:
For Domain Controllers on Windows 2016, the update is found here:
NOTE: Often these KB updates are packaged with other KB updates so these specific updates may not be listed in the Windows Update History console.
Current workaround is to manually enter the name of the users to be searched, and the expected results will return. For the actual solution please refer to the below articles:
On Server 2016 the KB can be removed or this update can be applied to resolve the issue.
On Server 2019 the KB can not be removed but this update can be applied to resolve the issue.
NOTE: The updates may no longer be available as they frequently get packaged into other KB's. Contact Microsoft to get more details on which one is needed to fix the issue previously found in the NetQueryDisplayInformation API.
In all versions of Enterprise Vault 12.x, when performing functions that call the NetQueryDisplayInformation API (or WinNT provider equivalent) that list users only the first page of data, often 50 or 100 entries is actually returned.