If you are working with Tableau Support then I recommend you continue working with them.
Thank you Mark Wu for Quick response, my Tableau Server version is 2018.1.4 Windows Server 2012 R2 (Pre TSM).
I had working(was able to import users from Active Directory into Tableau) server somehow in the middle something changed and now I am not able to import AD users.
Then I tried re-installing Tableau server but this time I hang at "Create Tableau Administrator" stage here admin user I am using Tableau server Run as Account.
Installation looks good tabadmin status -v says all the services are up and running.
Why I am asking here is if someone already faced similar issue they can give their insight and that helps me resolving my issue faster.
I think looking and searching it has something to do with GPO policy issue, any insight is appreciated.
Thank you Toby for the direction, I will keep that in my mind next time.
Since you are re-installing your server, why not try to install V2019.1 instead to see how it goes? BTW, all my 3 servers are on V2019.1 that works great!