Getting error "Your session has ended. Enter your password to log back in." every 30 seconds or so
Thanks for the troubleshooting help. It appears as though the issue was the cache and how Craft handles sessions.

For those who use a cache/CDN and are having issues with control panel session timeout:

Even after ignoring /admin on our cache, the cached pages on the public-facing portion of the site were conflicting somehow with how Craft was handling the sessions in the admin panel.

Our solution was to create a cookie we called isAuth that was created on login and destroyed on logout. We did this by creating a plugin and using userSession.onLogin and userSession.onLogout.

Then we set our Akamai cache to no-cache, no-store if isAuth cookie is present. This fixed all timeout issues.