Never heard of anything like that before, and don’t have a clue how you could make that happen if you wanted to!
Is this a one time occurrence, or something that happens with one user all the time? Can you see this happening for that user with other users Hosting? Do you have any other users that can’t get in to your session for 30 minutes? What indication does the user get – there has to be some error message or something.
If you can do those simple (but admittedly time consuming!) tests, we might be able to help you.