Hello!!
I'm having an issue after upgrading from Jira Server 7.6.1 to Jira Server 8.1. After the upgrade I replaced the server.xml file with the one I used in 7.6.1 in order to retain my proxy server settings. This worked and users are now able to login on the HTTPs portion of it but when I as an admin attempt to login on the backend HTTP localhost site the screen flashes once and goes back to the login page. The credentials arent wrong because when I purposefully type in the wrong password it tells me that my username/password are incorrect. This issue doesn't tell me anything but redirect me to the login page. I've uploaded a screenshot of what the logs say after this occurs.

Hope this helps. Any assistance would be appreciated; Cheers.