It is really unlikely that is a FOSSBilling issue.
CTRL + F5 is clearing your browser cache and the only two places where FOSSBilling does anything to determine how a browser would cache something from is is with the IPN callbacks and API endpoints.
Both of these locations send headers to explicitly tell the browser to not cache that data and that it must always re-validate it.
So that means the issues is almost certain coming from one of these things:
- A poorly configured browser
- A poorly configured webserver
- A poorly configure CDN
In all cases, only static assets like CSS, JS, and images should be getting cached so any config that goes past it (IE: the actual page contents) is an overzealous caching configuration that won't work correctly with FOSSBilling.