Log out & Log in back to check if the problem persists
After a cache flush, users may see slower performance the first time after the flush navigating in PPM.
If you have multiple Application servers you may need to apply the above steps to all Application servers.
For Clarity PPM SaaS customers:
When you navigate to security.caches page it gives you an application server host name. So connect to the application server in incognito mode or different browsers to get to the second APP server to flush caches if it is needed (though typically when you flush the cache on one app server, it will flush all PPM caches.