If you've recently made significant changes to the look and feel of your site, you're probably wanting to see how new users are experiencing those changes.
Fullstory checks for the Cache-Control header that the server responds with when we first fetch resources, which determines how long we cache resources. If your CSS styles appear out of date in your recordings, this could be the reason. You may want to check how you're serving your new CSS files, as well as the expiration date on your old CSS file headers.
With respect to adjusting how resources are served, check out this resource from the Google Chrome Developer Relations team: Prevent unnecessary network requests with the HTTP Cache.