I was getting both of these errors whilst trying to log in:
“Encountered an error while refreshing tocken for {username}” for accounts already added to launcher.
“There was an error while validating your account, please try again” for accounts not added to launcher.
Also the log in process seemed to hang with the blue ‘Starting Client’ bar at 50%.
All issues were solved by updating my network card drivers under device manager.
Hope that helps some others.