In looking at performance and page load, I noticed that some JS and CSS hosted by uPortal don't have the cache-control HTTP header set so the browser does an HTTP GET and gets back an HTTP 304.
These files are static and should be cached so the browser doesn't request the pages.
I did some initial troubleshooting and I see that the portal is adding cache-control headers, but they are somehow removed. When the browser requests the pages they are pulled from a cache in the portal with the http headers, but again the cache-control headers are lost.
Make sure you do not launch Tomcat with -Dorg.jasig.resourceserver.utils.aggr.aggregated_theme=false
Clear your browser's cache
Enable your developer tools on your browser to see network traffic, preferably retaining network requests
Login as admin. Note the requests should all be HTTP 200
Click on one of the tabs. Review the browser network traffic. You'll see requests to a few uPortal static assets (css, js) that receive a 304 response. These assets should have been set with a cache control header when first fetched (when you first logged in) so the browser fetches from cache without making an additional request.