After the error on-premise server, the AD-connect program along with the connected programs had been removed. Prior to the error all the systems where working fine.
(this Single AD Forest using pass-through authentication) with MFA enabled with seamless sign on enabled
After the reinstall of the same verion of AD connect.
The error generate was "Unable to validate credentials due to an unexpected error, Restart Azure AD connect with/interactiveAuth Option to further diagnose the issue"
Also connect using the global admin details on the PC's connected to local domain.
Error from the landing page is "Sorry,that didn't work, Please go back to office.com and try again. thanks"
The connected users are still operational, the exchange server on cloud still work