Very slow login for Registered Users on v188.8.131.52 site
On a (v184.108.40.206) site I have advanced permissions switched on. Nothing complex regarding the users, just normal 'Administrators' who have access to the dashboard etc, and other 'registered' users who have additional access to specific private front-end pages. Recently the 'registered' users take a very long time to login - almost exactly around 2 minutes. Once they are logged in they can move around the site as normal, at usual speed. The admin users can login at the usual speed. The site is running on a fast dedicated server with no other performance issues.
Has anyone else ever had this happen? - or - Can anyone suggest a possible course of action/investigation?