@Tobias

I'm not sure who to tell this to, but this error message came up tonight after I ran git pull and so on.
PHP Fatal error: Uncaught Error: Undefined constant "REGISTER_OPEN" in /Friendica_Directory/config/local.config.php:27

I switched REGISTER_OPEN back to \Friendica\Module\Register::OPEN then ran bin/console.php maintenance 0 and things worked right again.