Here are some of the highlights of the release v3.12.
See the detailed changelog for a complete list of changes.

For historical reasons (there was no admin role back in the nagios days) Thruk granted the admin role if you have both, the system_commands and the configuration_information role from the cgi.cfg.

Since this is not ideal and there is an admin role for quite some time now, it is time to change. In a future version only contacts will get the admin role from explicitly assigning them in the cgi.cfg and not from the 2 roles mentioned above.

If you want to disable this behavior now already. You can set admin_role_from_system_and_conf=0. For now this is still enabled by default.

The agents plugin introduced with in v3.10 is a config tool extension and can be used
to manage SNClient installations.
Note: you need to enable this plugin first, it is not enabled by default.

There had been many changes in this plugin to add support for the latest new check plugins in the snclient agent. It is now also possible to set additional naemon attributes for the resulting services.

The SNClient is a multi-platform agent designed to replace NSClient++ and NRPE.
Read more here:

When using multiple backends and none of them is available Thruk would show an error page. Now this has changed and the normal page would be shown, except it is empty. On top the backends will be listed in red.

In this case the backends bar will always be displayed, even if Thruk only uses a single backend.