Hi,
Please try the below steps and update the status.
1 Type the complete username while trying to login.
2 Make sure that Kerberos (GSSAPI) authentication is supported in your AD environment.
3 Try default port 636 and verify, if that works.
4 Ping the domain controller from your Skyline collector (nc -vz 1.1.1.1 636) and confirm if the port is open.