I am running 8.12 multiple sites and see no issues with it as I just did a install as late as a couple hours for a new customer so you would need to pass info to me to take a look.
You are using 8.0 and have not ran the required upgrade script for 8.0-8.1
Your version in the pp_settings table says 8.0 and none of the new settings for 8.1 exist as well as the new captcha field for the usergroups table which is why you can not be properly authenticated.