Another member shows as logged in

Any time our members go to the login page, it shows someone else logged in. Logging out takes you to the home page, but going back to the login shows that same person logged in still. But you can’t access the files, etc. We tried and tried to get around it, and suddenly it started working as usual. But a day later and it’s doing the same thing again.

The page I need help with: [log in to see the link]