User had access to Orion, but suddenly lost it. AD integration is in place

Have the users changed their AD passwords recently?

You can try disabling auto-login for those accounts/groups and have them try logging in again.  Or remove them from the AD group (if you're using groups) and create a temporary group or add their accounts individually into NPM and verify if they're able to login that way.

Also have them clear out their cookies and/or try a different browser - preferably Firefox since it's not reliant on the Windows Internet Options settings, just in case there's an issue in the Windows IE Options.

if the password is changed, does it not sync? Also it didnt happen for all users, just 3-4.

Not sure if any changes were made to their id's in AD

Ok, let me try for the cache clear option. But do we have any log file where we can check the login attempts or failures?

Well it turned out to be an issue for a specific location where AD connection is not in place.

Hence resolved it by providing individual access.

and got the audit logs enabled, it was in disabled state in web console settings.