After upgrading Jenkins to 2.528.1 from 2.516.3, Jenkins does not come up. We get 500 errors attempting to reach it. After removing security, it comes up, but then fails to be login. As it stands, unable to get the upgrade to work on any host. 

Using Linux and standard install methods. Not sure how to troubleshoot this issue. 

Jenkins is just unavailable. Only way to get it to work properly is turn off security.