You need to disable any caching you have set for that page. Usually things like that happen when you have some sort of caching plugin designed to help speed up your site by caching html and other data to make the pages load faster. If you have a caching plugin, then you need to look through its settings to see if you can disable it on specific pages or posts or for certain content types.
Other times, your hosting provider may have set you up with some server side caching that will cache often used database queries to speed things up, in which case the query that gets the signups may not return the most recent data.
Usually it’s the first, some sort of caching plugin. Server side caching is a bit more rare and usually also requires a plugin to take advantage of it with WordPress.