Hi David,
I had similar issues, with the 5.10 beta and final. These were related to browser caching and cookies. Clearing the browser cache solved most of those issues. I have Chrome configured (with an extension) to clear the cache each time I close the browser.
One remains, which is by design I’m afraid:
Our production project does not use the full page login but a popup. Most demo projects that use security, including the Employee and Expense demo’s, use a full page login because they support the appcloud login. This is controlled by index.html, which sets a cookie to force the full page login. Because the cookie is set at localhost, it affects all other projects too. When I get the full page login in my production project, I just kill the localhost cookies. This affects local testing only of course. Cloud nodes all have a separate URL, so the cookies are stored separately too.