WARNING: Portal for ArcGIS cannot connect to Active Directory LDAP server at ldaps

[ZacharyHart]

 We use Active Directory authentication (not using LDAP). There are two errors in sequence; see below.

• The only other post I've found related to this involves IWA.
• I have been assured by our IT provider that all Domain Controllers are Global Catalog Servers.
• We don't have any authentication issues as a result of this, but it is a curious and troubling warning.

[ChristopherPawlyszyn]

Have you tried connecting to the LDAPS port for global catalogs (3269) using another method such as ldp.exe?

Ldp | Microsoft Docs
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/cc...

That may give you some more information about why the connection is failing. With a connection reset error, it is possible the connection is being blocked by or timing-out on a firewall (either internal or external to the domain controller in question). The Active Directory connection does use LDAP to query the AD structure for users/groups, and connections will be made on 3269, 3268, 636, and 389, depending on whether LDAPS is configured with a proper certificate and the binding options set within group policy.

[jschuckert]

I am having this same error and the one new user to the organization (City) is unable to log into Portal. All other users have access as expected. 

Did you ever find a resolution?

Jared