is_logged_in_using_ipbl on initial page load through EZProxy

I have a website being accessed via EZProxy at some libraries. When the user initially logs in, the is_logged_in_using_ipbl() function doesn’t appear to be working and the users are able to view a menu that should be hidden.

I know this is a niche case, but is there any potential cause of what would be the issue on initial load?

Thanks!