Login Plugin: Registration not working

I have installed a new Grav-instance, enabled the user registration in the Plugins section in the admin backend and set the Registration path to /register. Everything else is default. When I now open domain.tld/register I see the "Register" heading but nothing else, no form is showing up.

What am I doing wrong?

Handling in GitHub on https://github.com/getgrav/grav-plugin-login/pull/97